test java

/** CastTest.java */

public class CastTest

{

    class A{}

    public static void main(String args[])

    {

        A a = new A();

    }

}

輸出結果:

CastTest.java:7: error: non-static variable this cannot be referenced from a
static context
        A a = new A();
              ^
1 error

我不懂，哪裡錯了?

若是把 class A 寫在外面，就過了

/** CastTest2.java */

class A{}

public class CastTest

{

    public static void main(String args[])

    {

        A a = new A();

    }

}