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The instanceof keyword returns true if what’s on the left is a class, subclass or interface of what’s on the right. Like this:
someObject instanceof someClass;
This lets you quickly check if an object is related to another class or interface! I honestly don’t use it very often, but it can be very helpful for certain situations.
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no enclosing instance of type 주제에 대한 자세한 내용은 여기를 참조하세요.
What causes error “No enclosing instance of type Foo is …
I get No enclosing instance of type Hello is accessible.” at the line that creates a new Thing. I’m guessing either: I have system level problems (either in …
Source: stackoverflow.com
Date Published: 8/2/2022
View: 2757
No enclosing instance of type is accessible – Yawin Tutor
The java No enclosing instance of type is accessible. Must qualify the allocation with an enclosing instance of type (e.g. x.new A() where x is an instance …
Source: www.yawintutor.com
Date Published: 10/7/2021
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java – What causes error “No enclosing instance of type Foo is …
Top 5 Answer for java – What causes error “No enclosing instance of type Foo is accessible” and how do I fix it? · Move Thing out of the Hello . · Change …
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Date Published: 5/25/2021
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Java Error: No enclosing instance of type Main is accessible …
The following error occurred today while compiling a Java program. No enclosing instance of type Main is accessible.
Source: programmerah.com
Date Published: 6/15/2022
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Java – No enclosing instance of type Foo is accessible
I get No enclosing instance of type Hello is accessible.” at the line that creates a new Thing. I’m guessing either:.
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No enclosing instance of type is accessible. Must qualify the …
ERROR – No enclosing instance of type is accessible. Must qualify the allocation with an enclosing instance of type (e.g. x.new A() where x is an instance of ).
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No Enclosing Instance Of Type Is Accessible – FaqCode4U.com
No enclosing instance of type is accessible. Tags: java , static-methods , multithreading , thread-safety Answers: | Viewed 41,366 times.
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No enclosing instance of type Class is accessible
Sáng nay ngồi code chơi gặp tình huống thế này. public A { public B{ private int num; public Date() { num = 0; } } public static …
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What causes error “No enclosing instance of typ…anycodings
Answers 1 : of What causes error No enclosing instance of type Foo is accessible and how do I fix it. static Thing will make your anycodings_java program …
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Java mutation error: no enclosing instance of type XXX is …
The meaning of error is , There are no external instances that can be accessed enclosing instance. You must assign an appropriate external …
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주제와 관련된 이미지 no enclosing instance of type
주제와 관련된 더 많은 사진을 참조하십시오 instanceof Java Keyword Tutorial. 댓글에서 더 많은 관련 이미지를 보거나 필요한 경우 더 많은 관련 기사를 볼 수 있습니다.
주제에 대한 기사 평가 no enclosing instance of type
- Author: Alex Lee
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How do I fix No enclosing instance of type?
Solution 1
If the non static inner class is modified to the static inner class, the static method will provide access to the static inner class. Changing the non static to the static inner class would fix the exception.
Is not an enclosing class Java error?
In this situation the “not an enclosing class” error is due to incorrect use of this . this , within an instance method or constructor, refers to the current object. Using MainActivity. this is referring to the object MainActivity as if it were the current object but the current object is of type TestHandler .
What are nested classes in Java?
A nested class is a member of its enclosing class. Non-static nested classes (inner classes) have access to other members of the enclosing class, even if they are declared private. Static nested classes do not have access to other members of the enclosing class.
How do you initialize a static inner class in Java?
To instantiate an inner class, you must first instantiate the outer class. Then, create the inner object within the outer object with this syntax: OuterClass. InnerClass innerObject = outerObject.
How do you create an inner class in Java?
Creating an inner class is quite simple. You just need to write a class within a class. Unlike a class, an inner class can be private and once you declare an inner class private, it cannot be accessed from an object outside the class.
What are static classes?
A static class is basically the same as a non-static class, but there is one difference: a static class cannot be instantiated. In other words, you cannot use the new operator to create a variable of the class type.
How do you define a static class in Java?
A static inner class is a nested class which is a static member of the outer class. It can be accessed without instantiating the outer class, using other static members. Just like static members, a static nested class does not have access to the instance variables and methods of the outer class.
Is not an enclosing class Android Studio intent?
not an enclosing class error is thrown because of your usage of this keyword. this is a reference to the current object — the object whose method or constructor is being called. With this you can only refer to any member of the current object from within an instance method or a constructor.
Can we create immutable class in Java?
Immutable class in java means that once an object is created, we cannot change its content. In Java, all the wrapper classes (like Integer, Boolean, Byte, Short) and String class is immutable. We can create our own immutable class as well.
Can inner class be public?
Java inner class can be declared private, public, protected, or with default access whereas an outer class can have only public or default access.
What if a class is private?
Private classes are allowed, but only as inner or nested classes. If you have a private inner or nested class, then access is restricted to the scope of that outer class. If you have a private class on its own as a top-level class, then you can’t get access to it from anywhere.
Can static inner class have constructor?
All classes have constructors, and they’ll be default if you don’t declare one that’s non-default. static class means that you can instantiate this class in every context (not necessarily bound to a Reader1 ).
Can abstract class have inner class?
It does not matter whether your class is abstract or concrete, as long as the nested class is either public , protected or the subclass is in the same package and the inner class is package private (default access modifier), the subclass will have access to it.
Can static class private?
A static class is a class that is created inside a class, is called a static nested class in Java. It cannot access non-static data members and methods. It can be accessed by outer class name. It can access static data members of the outer class, including private.
What is nested class with example?
A nested class is a class that is declared in another class. The nested class is also a member variable of the enclosing class and has the same access rights as the other members. However, the member functions of the enclosing class have no special access to the members of a nested class.
Why do we use nested classes in Java?
As mentioned in the section Nested Classes, nested classes enable you to logically group classes that are only used in one place, increase the use of encapsulation, and create more readable and maintainable code.
What is the difference between inner class and nested class?
In Java programming, nested and inner classes often go hand in hand. A class that is defined within another class is called a nested class. An inner class, on the other hand, is a non-static type, a particular specimen of a nested class.
What is the difference between an inner class and a sub class?
inner classes are in the same file, whereas subclasses can be in another file, maybe in another package. You cannot get an instance of an inner class without an instance of the class that contains it. inner classes have the methods they want, whereas subclasses have the methods of their parent class.
What causes error “No enclosing instance of type Foo is accessible” and how do I fix it?
You’ve declared the class Thing as a non-static inner class. That means it must be associated with an instance of the Hello class.
In your code, you’re trying to create an instance of Thing from a static context. That is what the compiler is complaining about.
There are a few possible solutions. Which solution to use depends on what you want to achieve.
Move Thing out of the Hello class.
Change Thing to be a static nested class. static class Thing
Create an instance of Hello before creating an instance of Thing . public static void main(String[] args) { Hello h = new Hello(); Thing thing1 = h.new Thing(); // hope this syntax is right, typing on the fly 😛 }
The last solution (a non-static nested class) would be mandatory if any instance of Thing depended on an instance of Hello to be meaningful. For example, if we had:
public class Hello { public int enormous; public Hello(int n) { enormous = n; } public class Thing { public int size; public Thing(int m) { if (m > enormous) size = enormous; else size = m; } } … }
any raw attempt to create an object of class Thing , as in:
Thing t = new Thing(31);
would be problematic, since there wouldn’t be an obvious enormous value to test 31 against it. An instance h of the Hello outer class is necessary to provide this h.enormous value:
… Hello h = new Hello(30); … Thing t = h.new Thing(31); …
Because it doesn’t mean a Thing if it doesn’t have a Hello .
For more information on nested/inner classes: Nested Classes (The Java Tutorials)
No enclosing instance of type is accessible – Yawin Tutor
The java No enclosing instance of type is accessible. Must qualify the allocation with an enclosing instance of type (e.g. x.new A() where x is an instance of ). exception happens when an instance is created for an inner class in the outer class static method. The static method attempts to create an object of an inner class that belongs to an outer class instance.
The non static member variables cannot be accessed by a class static method. The instance of a non static inner class cannot be created by a static class method. Both the method and the inner class should be modified as static or both should not be static. Otherwise, the exception No enclosing instance of type is accessible. Must qualify the allocation with an enclosing instance of type (e.g. x.new A() where x is an instance of ). will be thrown.
The inner class scope will be the same as the class member variable. The inner class can be declared as a static class as a static member variable. The instance of a non static inner class will be created with in the outer class object. The instance of the inner static class would be accessible at the class level. It can then be created in both static and not static methods.
Exception
The java error message will be seen as below in the eclipse.
No enclosing instance of type Test is accessible. Must qualify the allocation with an enclosing instance of type Test (e.g. x.new A() where x is an instance of Test).
The stack trace of the exception will be shown as shown below.
Exception in thread “main” java.lang.Error: Unresolved compilation problem: No enclosing instance of type SubListTest is accessible. Must qualify the allocation with an enclosing instance of type SubListTest (e.g. x.new A() where x is an instance of SubListTest). at com.yawintutor.SubListTest.load(SubListTest.java:10) at com.yawintutor.SubListTest.main(SubListTest.java:6)
Root Cause
Static methods can have access to either static variables or static methods. Static methods could not have access to non static variables or non static methods. Static methods are not allowed to have access to a non static inner class. An exception will be thrown if a static method attempts to create an instance of a non static inner class.
How to reproduce this exception
When the static method tries to create an instance of a non static inner class, the static method creates an exception. The static method would not be allowed to access the inner class that belongs to the outer class object. The example below reproduces the exception No enclosing instance of type is accessible. Must qualify the allocation with an enclosing instance of type (e.g. x.new A() where x is an instance of ).
package com.yawintutor; public class SubListTest { public static void main(String[] args) { load(); } public static void load() { Department dept = new Department(); System.out.println(dept.getName()); } public class Department { public String name=”dept”; public String getName() { return name; } } }
Output
Exception in thread “main” java.lang.Error: Unresolved compilation problem: No enclosing instance of type SubListTest is accessible. Must qualify the allocation with an enclosing instance of type SubListTest (e.g. x.new A() where x is an instance of SubListTest). at com.yawintutor.SubListTest.load(SubListTest.java:10) at com.yawintutor.SubListTest.main(SubListTest.java:6)
Solution 1
If the non static inner class is modified to the static inner class, the static method will provide access to the static inner class. Changing the non static to the static inner class would fix the exception.
package com.yawintutor; public class SubListTest { public static void main(String[] args) { load(); } public static void load() { Department dept = new Department(); System.out.println(dept.getName()); } public static class Department { public String name=”dept”; public String getName() { return name; } } }
Output
dept
Solution 2
If the static method is modified to a non static method, both the method and the inner class would be within the scope of the object. The non static method can be used to access the non static inner class. In this case, the instance of the outer class will be used.
package com.yawintutor; public class SubListTest { public static void main(String[] args) { SubListTest subListTest = new SubListTest(); subListTest.load(); } public void load() { Department dept = new Department(); System.out.println(dept.getName()); } public class Department { public String name=”dept”; public String getName() { return name; } } }
Output
dept
Solution 3
If the inner class is created outside the outer class or in another file, the inner class would be created as a separate class in the package. The class is going to be created like any other class. The exception will not be thrown.
SubListTest.java
package com.yawintutor; public class SubListTest { public static void main(String[] args) { load(); } public static void load() { Department dept = new Department(); System.out.println(dept.getName()); } }
Department.java
package com.yawintutor; public class Department { public String name=”dept”; public String getName() { return name; } }
Output
dept
Solution 4
When an instance of a class is created once in a static method, an instance of an outer class is created in a static method. The instance of the inner class can be created using the object of the outer class.
package com.yawintutor; public class SubListTest { public static void main(String[] args) { load(); } public static void load() { SubListTest subListTest = new SubListTest(); Department dept = subListTest.new Department(); System.out.println(dept.getName()); } public class Department { public String name=”dept”; public String getName() { return name; } } }
Output
dept
Solution 5
When an instance of a class is created once in a static method, an instance of an outer class is created in a static method. The instance of the inner class can be created using the object of the outer class. This is an another way of creating instance of the inner class using the local variable.
package com.yawintutor; public class SubListTest { public static void main(String[] args) { load(); } public static void load() { Department dept = new SubListTest().new Department(); System.out.println(dept.getName()); } public class Department { public String name=”dept”; public String getName() { return name; } } }
Output
Error “is not an enclosing class”
I’m doing a Handler exercise just to test how it works, but I’m trying some problem I can not figure out.
This is my main class code:
public class MainActivity extends Activity { protected static final int MENSAGEM_TESTE = 1; private Handler handler = new TesteHandler(); Button button; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); button = (Button) findViewById(R.id.button); button.setText(“Atualizar o texto em 3 segundos”); button.setOnClickListener(new Button.OnClickListener(){ @Override public void onClick(View view) { //Cria msg com delay de 3 seg Message msg = new Message(); msg.what = MENSAGEM_TESTE; //Envia msg handler.sendMessageDelayed(msg, 3000); } }); } }
And this is the code for my class TesteHandler :
import static com.exercicios.handler.MainActivity.MENSAGEM_TESTE; public class TesteHandler extends Handler { @Override public void handleMessage(Message msg) { switch (msg.what) { case MENSAGEM_TESTE: Toast.makeText(MainActivity.this, “A mensagem chegou!”, Toast.LENGTH_SHORT).show(); break; } } }
Android Studio is returning me the following error:
‘com.exercicios.handler.MainActivity’ is not an enclosing class.
I’m not finding what I need to fix, can someone please give me a hand? Thank you in advance!
Nested Classes (The Java™ Tutorials > Learning the Java Language > Classes and Objects)
Trail: Learning the Java Language
Lesson: Classes and Objects
The Java Tutorials have been written for JDK 8. Examples and practices described in this page don’t take advantage of improvements introduced in later releases and might use technology no longer available. See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases. See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
Nested Classes
The Java programming language allows you to define a class within another class. Such a class is called a nested class and is illustrated here:
class OuterClass { … class NestedClass { … } }
Terminology: Nested classes are divided into two categories: non-static and static. Non-static nested classes are called inner classes. Nested classes that are declared static are called static nested classes.
class OuterClass { … class InnerClass { … } static class StaticNestedClass { … } }
A nested class is a member of its enclosing class. Non-static nested classes (inner classes) have access to other members of the enclosing class, even if they are declared private. Static nested classes do not have access to other members of the enclosing class. As a member of the OuterClass , a nested class can be declared private , public , protected , or package private. (Recall that outer classes can only be declared public or package private.)
Why Use Nested Classes?
Compelling reasons for using nested classes include the following:
It is a way of logically grouping classes that are only used in one place : If a class is useful to only one other class, then it is logical to embed it in that class and keep the two together. Nesting such “helper classes” makes their package more streamlined.
It increases encapsulation : Consider two top-level classes, A and B, where B needs access to members of A that would otherwise be declared private . By hiding class B within class A, A’s members can be declared private and B can access them. In addition, B itself can be hidden from the outside world.
It can lead to more readable and maintainable code: Nesting small classes within top-level classes places the code closer to where it is used.
Inner Classes
As with instance methods and variables, an inner class is associated with an instance of its enclosing class and has direct access to that object’s methods and fields. Also, because an inner class is associated with an instance, it cannot define any static members itself.
Objects that are instances of an inner class exist within an instance of the outer class. Consider the following classes:
class OuterClass { … class InnerClass { … } }
An instance of InnerClass can exist only within an instance of OuterClass and has direct access to the methods and fields of its enclosing instance.
To instantiate an inner class, you must first instantiate the outer class. Then, create the inner object within the outer object with this syntax:
OuterClass outerObject = new OuterClass(); OuterClass.InnerClass innerObject = outerObject.new InnerClass();
There are two special kinds of inner classes: local classes and anonymous classes.
Static Nested Classes
As with class methods and variables, a static nested class is associated with its outer class. And like static class methods, a static nested class cannot refer directly to instance variables or methods defined in its enclosing class: it can use them only through an object reference. Inner Class and Nested Static Class Example demonstrates this.
Note: A static nested class interacts with the instance members of its outer class (and other classes) just like any other top-level class. In effect, a static nested class is behaviorally a top-level class that has been nested in another top-level class for packaging convenience. A static nested class interacts with the instance members of its outer class (and other classes) just like any other top-level class. In effect, a static nested class is behaviorally a top-level class that has been nested in another top-level class for packaging convenience. Inner Class and Nested Static Class Example also demonstrates this.
You instantiate a static nested class the same way as a top-level class:
StaticNestedClass staticNestedObject = new StaticNestedClass();
The following example, OuterClass , along with TopLevelClass , demonstrates which class members of OuterClass an inner class ( InnerClass ), a nested static class ( StaticNestedClass ), and a top-level class ( TopLevelClass ) can access:
OuterClass.java
public class OuterClass { String outerField = “Outer field”; static String staticOuterField = “Static outer field”; class InnerClass { void accessMembers() { System.out.println(outerField); System.out.println(staticOuterField); } } static class StaticNestedClass { void accessMembers(OuterClass outer) { // Compiler error: Cannot make a static reference to the non-static // field outerField // System.out.println(outerField); System.out.println(outer.outerField); System.out.println(staticOuterField); } } public static void main(String[] args) { System.out.println(“Inner class:”); System.out.println(“————“); OuterClass outerObject = new OuterClass(); OuterClass.InnerClass innerObject = outerObject.new InnerClass(); innerObject.accessMembers(); System.out.println(”
Static nested class:”); System.out.println(“——————–“); StaticNestedClass staticNestedObject = new StaticNestedClass(); staticNestedObject.accessMembers(outerObject); System.out.println(”
Top-level class:”); System.out.println(“——————–“); TopLevelClass topLevelObject = new TopLevelClass(); topLevelObject.accessMembers(outerObject); } }
TopLevelClass.java
public class TopLevelClass { void accessMembers(OuterClass outer) { // Compiler error: Cannot make a static reference to the non-static // field OuterClass.outerField // System.out.println(OuterClass.outerField); System.out.println(outer.outerField); System.out.println(OuterClass.staticOuterField); } }
This example prints the following output:
Inner class: ———— Outer field Static outer field Static nested class: ——————– Outer field Static outer field Top-level class: ——————– Outer field Static outer field
Note that a static nested class interacts with the instance members of its outer class just like any other top-level class. The static nested class StaticNestedClass can’t directly access outerField because it’s an instance variable of the enclosing class, OuterClass . The Java compiler generates an error at the highlighted statement:
static class StaticNestedClass { void accessMembers(OuterClass outer) { // Compiler error: Cannot make a static reference to the non-static // field outerField System.out.println(outerField); } }
To fix this error, access outerField through an object reference:
System.out.println(outer.outerField);
Similarly, the top-level class TopLevelClass can’t directly access outerField either.
If a declaration of a type (such as a member variable or a parameter name) in a particular scope (such as an inner class or a method definition) has the same name as another declaration in the enclosing scope, then the declaration shadows the declaration of the enclosing scope. You cannot refer to a shadowed declaration by its name alone. The following example, ShadowTest , demonstrates this:
public class ShadowTest { public int x = 0; class FirstLevel { public int x = 1; void methodInFirstLevel(int x) { System.out.println(“x = ” + x); System.out.println(“this.x = ” + this.x); System.out.println(“ShadowTest.this.x = ” + ShadowTest.this.x); } } public static void main(String… args) { ShadowTest st = new ShadowTest(); ShadowTest.FirstLevel fl = st.new FirstLevel(); fl.methodInFirstLevel(23); } }
The following is the output of this example:
x = 23 this.x = 1 ShadowTest.this.x = 0
This example defines three variables named x : the member variable of the class ShadowTest , the member variable of the inner class FirstLevel , and the parameter in the method methodInFirstLevel . The variable x defined as a parameter of the method methodInFirstLevel shadows the variable of the inner class FirstLevel . Consequently, when you use the variable x in the method methodInFirstLevel , it refers to the method parameter. To refer to the member variable of the inner class FirstLevel , use the keyword this to represent the enclosing scope:
System.out.println(“this.x = ” + this.x);
Refer to member variables that enclose larger scopes by the class name to which they belong. For example, the following statement accesses the member variable of the class ShadowTest from the method methodInFirstLevel :
System.out.println(“ShadowTest.this.x = ” + ShadowTest.this.x);
Nested Classes in Java
In Java, it is possible to define a class within another class, such classes are known as nested classes. They enable you to logically group classes that are only used in one place, thus this increases the use of encapsulation, and creates more readable and maintainable code.
The scope of a nested class is bounded by the scope of its enclosing class. Thus in below example, class NestedClass does not exist independently of class OuterClass.
A nested class has access to the members, including private members, of the class in which it is nested. The reverse is also true i.e., the enclosing class can access the members of the nested class.
A nested class is also a member of its enclosing class.
As a member of its enclosing class, a nested class can be declared private, public, protected, or package private(default).
Nested classes are divided into two categories: static nested class : Nested classes that are declared static are called static nested classes. inner class : An inner class is a non-static nested class.
Syntax:
class OuterClass { … class NestedClass { … } }
Static nested classes
In the case of normal or regular inner classes, without an outer class object existing, there cannot be an inner class object. i.e., an object of the inner class is always strongly associated with an outer class object. But in the case of static nested class, Without an outer class object existing, there may be a static nested class object. i.e., an object of a static nested class is not strongly associated with the outer class object.
As with class methods and variables, a static nested class is associated with its outer class. And like static class methods, a static nested class cannot refer directly to instance variables or methods defined in its enclosing class: it can use them only through an object reference.
They are accessed using the enclosing class name.
OuterClass.StaticNestedClass
For example, to create an object for the static nested class, use this syntax:
OuterClass.StaticNestedClass nestedObject = new OuterClass.StaticNestedClass();
class OuterClass { static int outer_x = 10 ; int outer_y = 20 ; private static int outer_private = 30 ; static class StaticNestedClass { void display() { System.out.println( “outer_x = ” + outer_x); System.out.println( “outer_private = ” + outer_private); } } } public class StaticNestedClassDemo { public static void main(String[] args) { OuterClass.StaticNestedClass nestedObject = new OuterClass.StaticNestedClass(); nestedObject.display(); } }
Output:
outer_x = 10 outer_private = 30
Inner classes
To instantiate an inner class, you must first instantiate the outer class. Then, create the inner object within the outer object with this syntax:
OuterClass.InnerClass innerObject = outerObject.new InnerClass();
There are two special kinds of inner classes :
class OuterClass { static int outer_x = 10 ; int outer_y = 20 ; private int outer_private = 30 ; class InnerClass { void display() { System.out.println( “outer_x = ” + outer_x); System.out.println( “outer_y = ” + outer_y); System.out.println( “outer_private = ” + outer_private); } } } public class InnerClassDemo { public static void main(String[] args) { OuterClass outerObject = new OuterClass(); OuterClass.InnerClass innerObject = outerObject. new InnerClass(); innerObject.display(); } }
Output:
outer_x = 10 outer_y = 20 outer_private = 30
Comparison between normal or regular class and static nested class
S.NO Normal/Regular inner class Static nested class 1. Without an outer class object existing, there cannot be an inner class object. That is, the inner class object is always associated with the outer class object. Without an outer class object existing, there may be a static nested class object. That is, static nested class object is not associated with the outer class object. 2. Inside normal/regular inner class, static members can’t be declared. Inside static nested class, static members can be declared. 3. As main() method can’t be declared, regular inner class can’t be invoked directly from the command prompt. As main() method can be declared, the static nested class can be invoked directly from the command prompt. 4. Both static and non static members of outer class can be accessed directly. Only a static member of outer class can be accessed directly.
No enclosing instance of type is accessible – Yawin Tutor
The java No enclosing instance of type is accessible. Must qualify the allocation with an enclosing instance of type (e.g. x.new A() where x is an instance of ). exception happens when an instance is created for an inner class in the outer class static method. The static method attempts to create an object of an inner class that belongs to an outer class instance.
The non static member variables cannot be accessed by a class static method. The instance of a non static inner class cannot be created by a static class method. Both the method and the inner class should be modified as static or both should not be static. Otherwise, the exception No enclosing instance of type is accessible. Must qualify the allocation with an enclosing instance of type (e.g. x.new A() where x is an instance of ). will be thrown.
The inner class scope will be the same as the class member variable. The inner class can be declared as a static class as a static member variable. The instance of a non static inner class will be created with in the outer class object. The instance of the inner static class would be accessible at the class level. It can then be created in both static and not static methods.
Exception
The java error message will be seen as below in the eclipse.
No enclosing instance of type Test is accessible. Must qualify the allocation with an enclosing instance of type Test (e.g. x.new A() where x is an instance of Test).
The stack trace of the exception will be shown as shown below.
Exception in thread “main” java.lang.Error: Unresolved compilation problem: No enclosing instance of type SubListTest is accessible. Must qualify the allocation with an enclosing instance of type SubListTest (e.g. x.new A() where x is an instance of SubListTest). at com.yawintutor.SubListTest.load(SubListTest.java:10) at com.yawintutor.SubListTest.main(SubListTest.java:6)
Root Cause
Static methods can have access to either static variables or static methods. Static methods could not have access to non static variables or non static methods. Static methods are not allowed to have access to a non static inner class. An exception will be thrown if a static method attempts to create an instance of a non static inner class.
How to reproduce this exception
When the static method tries to create an instance of a non static inner class, the static method creates an exception. The static method would not be allowed to access the inner class that belongs to the outer class object. The example below reproduces the exception No enclosing instance of type is accessible. Must qualify the allocation with an enclosing instance of type (e.g. x.new A() where x is an instance of ).
package com.yawintutor; public class SubListTest { public static void main(String[] args) { load(); } public static void load() { Department dept = new Department(); System.out.println(dept.getName()); } public class Department { public String name=”dept”; public String getName() { return name; } } }
Output
Exception in thread “main” java.lang.Error: Unresolved compilation problem: No enclosing instance of type SubListTest is accessible. Must qualify the allocation with an enclosing instance of type SubListTest (e.g. x.new A() where x is an instance of SubListTest). at com.yawintutor.SubListTest.load(SubListTest.java:10) at com.yawintutor.SubListTest.main(SubListTest.java:6)
Solution 1
If the non static inner class is modified to the static inner class, the static method will provide access to the static inner class. Changing the non static to the static inner class would fix the exception.
package com.yawintutor; public class SubListTest { public static void main(String[] args) { load(); } public static void load() { Department dept = new Department(); System.out.println(dept.getName()); } public static class Department { public String name=”dept”; public String getName() { return name; } } }
Output
dept
Solution 2
If the static method is modified to a non static method, both the method and the inner class would be within the scope of the object. The non static method can be used to access the non static inner class. In this case, the instance of the outer class will be used.
package com.yawintutor; public class SubListTest { public static void main(String[] args) { SubListTest subListTest = new SubListTest(); subListTest.load(); } public void load() { Department dept = new Department(); System.out.println(dept.getName()); } public class Department { public String name=”dept”; public String getName() { return name; } } }
Output
dept
Solution 3
If the inner class is created outside the outer class or in another file, the inner class would be created as a separate class in the package. The class is going to be created like any other class. The exception will not be thrown.
SubListTest.java
package com.yawintutor; public class SubListTest { public static void main(String[] args) { load(); } public static void load() { Department dept = new Department(); System.out.println(dept.getName()); } }
Department.java
package com.yawintutor; public class Department { public String name=”dept”; public String getName() { return name; } }
Output
dept
Solution 4
When an instance of a class is created once in a static method, an instance of an outer class is created in a static method. The instance of the inner class can be created using the object of the outer class.
package com.yawintutor; public class SubListTest { public static void main(String[] args) { load(); } public static void load() { SubListTest subListTest = new SubListTest(); Department dept = subListTest.new Department(); System.out.println(dept.getName()); } public class Department { public String name=”dept”; public String getName() { return name; } } }
Output
dept
Solution 5
When an instance of a class is created once in a static method, an instance of an outer class is created in a static method. The instance of the inner class can be created using the object of the outer class. This is an another way of creating instance of the inner class using the local variable.
package com.yawintutor; public class SubListTest { public static void main(String[] args) { load(); } public static void load() { Department dept = new SubListTest().new Department(); System.out.println(dept.getName()); } public class Department { public String name=”dept”; public String getName() { return name; } } }
Output
java – What causes error “No enclosing instance of type Foo is accessible” and how do I fix it?
You’ve declared the class Thing as a non-static inner class. That means it must be associated with an instance of the Hello class.
In your code, you’re trying to create an instance of Thing from a static context. That is what the compiler is complaining about.
There are a few possible solutions. Which solution to use depends on what you want to achieve.
Move Thing out of the Hello class.
Change Thing to be a static nested class. static class Thing
Create an instance of Hello before creating an instance of Thing . public static void main(String[] args) { Hello h = new Hello(); Thing thing1 = h.new Thing(); // hope this syntax is right, typing on the fly 😛 }
The last solution (a non-static nested class) would be mandatory if any instance of Thing depended on an instance of Hello to be meaningful. For example, if we had:
public class Hello { public int enormous; public Hello(int n) { enormous = n; } public class Thing { public int size; public Thing(int m) { if (m > enormous) size = enormous; else size = m; } } … }
any raw attempt to create an object of class Thing , as in:
Thing t = new Thing(31);
would be problematic, since there wouldn’t be an obvious enormous value to test 31 against it. An instance h of the Hello outer class is necessary to provide this h.enormous value:
… Hello h = new Hello(30); … Thing t = h.new Thing(31); …
Because it doesn’t mean a Thing if it doesn’t have a Hello .
For more information on nested/inner classes: Nested Classes (The Java Tutorials)
Java Error: No enclosing instance of type Main is accessible. Must qualify the allocation with an encl
The following error occurred today while compiling a Java program.
No enclosing instance of type Main is accessible. Must qualify the allocation with an enclosing instance of type Main (e.g. x.new A() where x is an instance of Main).
The source code I originally wrote looked like this
public class Main { class Dog { private String name; private int weight; public Dog(String name, int weight) { this.setName(name); this.weight = weight; } public int getWeight() { return weight; } public void setWeight(int weight) {this.weight = weight;} public void setName(String name) {this.name = name;} public String getName() {return name;} } public static void main(String[] args) { Dog d1 = new Dog(“dog1”,1); } }
When this error occurred, I didn’t quite understand it.
After learning from other people’s explanation, I suddenly realized.
In the code, my dog class is an internal class defined in main. The dog inner class is dynamic, while my main method is static.
Just as static methods cannot call dynamic methods.
There are two solutions:
Method 1
Define the inner class dog as a static class.
Method 2
Define the inner class dog outside the main class.
Read More:
No enclosing instance of type Foo is accessible
I have the following code:
class Hello { class Thing { public int size; Thing() { size = 0; } } public static void main(String[] args) { Thing thing1 = new Thing(); System.out.println(“Hello, World!”); } }
I know Thing does nothing, but my Hello, World program compiles just fine without it. It’s only my defined classes that are failing on me.
And it refuses to compile. I get No enclosing instance of type Hello is accessible.” at the line that creates a new Thing. I’m guessing either:
I have system level problems (either in DrJava or my Java install) or
I have some basic misunderstanding of how to construct a working program in java.
Any ideas?
No Enclosing Instance Of Type Is Accessible
Tags: java , static-methods , multithreading , thread-safety Answers: | Viewed 41,366 times
This question already has answers here:
What causes error “No enclosing instance of type Foo is accessible” and how do I fix it?
(8 answers)
Closed 8 years ago .
The whole code is:
public class ThreadLocalTest {
ThreadLocal
globalint = new ThreadLocal (){ @Override
protected Integer initialValue() {
return new Integer(0);
}
};
public class MyThread implements Runnable{
Integer myi;
ThreadLocalTest mytest;
public MyThread(Integer i, ThreadLocalTest test) {
myi = i;
mytest = test;
}
@Override
public void run() {
System.out.println(“I am thread:” + myi);
Integer myint = mytest.globalint.get();
System.out.println(myint);
mytest.globalint.set(myi);
}
}
public static void main(String[] args){
ThreadLocalTest test = new ThreadLocalTest();
new Thread(new MyThread(new Integer(1), test)).start();
}
}
why the following snippet:
ThreadLocalTest test=new ThreadLocalTest();
new Thread(new MyThread(new Integer(1),test)).start();
cause the following error:
No enclosing instance of type ThreadLocalTest is accessible. Must qualify the
allocation with an enclosing instance of type ThreadLocalTest (e.g. x.new A()
where x is an instance of ThreadLocalTest).
The core problem is that:
i want to initialize the inner class in the static methods.
here are two solutions:
make the inner class as outer class
use outer reference like :
No enclosing instance of type Class is accessible
Sáng nay ngồi code chơi gặp tình huống thế này.
public class A { public class B{ private int num; public Date() { num = 0; } } public static void main(String[] args) { B b = new B(); } }
Dính ngay lỗi:
No enclosing instance of type A is accessible. Must qualify the allocation with an enclosing instance of type A(e.g. x.new B() where x is an instance of A)
Do lớp B là inner class của lớp A mà khi cần thì không thể truy xuất trực tiếp lớp B. Phải khi báo lớp A rồi hãy gọi B thông qua A.
Lý giải sâu hơn:
static class B will make your program work.
As it is, you’ve got B as an inner class, which (by definition) is associated with a particular instance of A (even if it never uses or refers to it), which means it’s an error to say new B(); without having a particular A instance in scope.
If you declare it as a static class instead, then it’s a “nested” class, which doesn’t need a particular A instance.
Giải quyết:
Cách 1:
A a = new A();
B b = a.new B();
Cách 2:
thêm từ khóa static lúc khai báo lớp B.
==> Thật là khó để tìm hiểu hết các vấn đề phải không bạn 🙂
키워드에 대한 정보 no enclosing instance of type
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