接口 -> 匿名 class

Question

Why does the following code not print ??? ?

public class TestInterface {
    interface I {};
    I tester = new I() {{System.out.println("???");}};
    static public void main(String[]args){
        System.out.println("OGOGO");
    }
}

Output:

OGOGO

• IDE: IntelliJ
• Jave: jdk-14.0.2

Answer 1

It doesn't print because new I() {{System.out.println("???");}}; is never executed. Notice that you have a member variable , a field, no static , there. Fields are initialized together with the corresponding instance of the class, here TestInterface . If you want it to print something, create an instance of TestInterface and its fields will get initialized with what you've specified. Or simply mark it with static so it becomes a class variable and is initialized when the class itself is initialized.

Answer 2

akuzminykh is right!

When I change to

static I tester

it prints.