problem creating object of inner class in java
Solution 1
InnerClass
needs to be static
itself, i.e.
public class Test {
static class InnerClass{
}
public static void main(String[] args){
InnerClass ic = new InnerClass();
}
}
If InnerClass
is not static
, it can only be instantiated in the context of a parent instance of Test
. The rather baroque syntax for this is:
public class Test {
class InnerClass{
}
public static void main(String[] args){
Test test = new Test();
InnerClass ic = test.new InnerClass();
}
}
Solution 2
Your inner class depends on an instance of the Test
class. main is a static method, thus you can't create an instance of InnerClass
.
I think you want to declare your inner class as static
:
class Test {
static class InnerClass { }
public static void main(String[] args){
InnerClass ic = new InnerClass();
}
}
More information about nested classes : http://download.oracle.com/javase/tutorial/java/javaOO/nested.html
Short explanation
There's mainly two types of nested classes : "static nested class" and "inner class"
Static nested class are used to logically group two classes and can be used to increase encapsulation. They can be used like any other classes and, except for visibility, they don't have any particular access to the outer class fields. They can logically be instantiated in a static context.
Inner class (ie not static) are bound to a particular instance of the outer class. This means you must have an instance of the outer class to instantiate the inner class. Have a look at Skaffman second code chunk for an instantiation example. Since inner classes are bound to an instance of the outer class, they have access to every field relative to this particular instance.
I hope all this is now clearer.
bunkdeath
Updated on June 11, 2022Comments
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bunkdeath about 2 years
Here is the code.public class Test { class InnerClass{ } public static void main(String[] args){ InnerClass ic = new InnerClass(); } }
It says the error message
non-static variable this cannot be referenced from a static context after creation of object ic.
Can anyone give me the reason?
Thanks
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Saurabh Gokhale over 13 years
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user1923551 over 10 yearsmain is a static method, it can access only other static members of outer class.
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bunkdeath over 13 yearsDeclaring InnerClass to static works, I tried it according to the error message. But still I didn't get why. Can you explain more?
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krtek over 13 years@bunkdeath the given link should be enough to understand the reason, but i'll update my answer a bit. @herbalessence skaffman doesn't explain anything, he just gives working code.
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AZ_ over 10 yearsyou can do it in one line too " InnerClass ic1 = new Test().new InnerClass(); "