第十道Java小问题

以下程序中编译时会出错的是
1)

public class A {
    final int[] a = new int[0];

    public A() {
    }

    public static void main(String[] args) {
        A a = new A();
        a.a[0] = 2;
    }

}

 

2)

public class A {
    final int[] a;

    public A() {
        a = new int[0];
    }

    public static void main(String[] args) {
        A a = new A();
    }

}

 

3)

public class A {
    final int[] a;

    public A() {
    }

    public static void main(String[] args) {
        A a = new A();
        a.a = new int[0];

    }

}

 

4)

public class A {
    final int[] a = new int[0];

    public A() {
        int a;
        int b = a;
    }

    public static void main(String[] args) {
        A a = new A();

    }

}