How to load nested classes in Java?

问题:

I have the following java code:

public class CheckInnerStatic {

private static class Test {
    static {
        System.out.println("Static block initialized");
    }
    public Test () {
        System.out.println("Constructor called");
    }
}

    public static void main (String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {
        System.out.println("Inside main");
        Class.forName("Test");    // Doesn't work, gives ClassNotFoundException
        //Test test = new Test();   // Works fine
    }
}

Why doesn't the class.forName("Test") work here while the next line works fine?

回答1:

Use Outer$Nested (regardless if nested class is static or not)

public class CheckInnerStatic {

    private static class Test {
    static {
        System.out.println("Static block initialized");
    }
    public Test () {
        System.out.println("Constructor called");
    }
}

    public static void main (String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {
        System.out.println("Inside main");
        Class<?> cls = Class.forName("CheckInnerStatic$Test");
        //Test test = new Test();
    }
}

回答2:

You need to use the fully qualified class name, i.e. yourpackage.CheckInnerStatic$Test (assuming you defined a package, otherwise skip that part).

回答3:

Class innerClass = Class.forName("com.foo.OuterClass$InnerClass");