java主类内部如何声明内部类

Question

求原因？

import java.util.Scanner;

public class Test {

// public static void ()

static class Dian {

int x;

int y;

public int getX() {

return x;

}

public void setX(int x) {

this.x = x;

}

public int getY() {

return y;

}

public void setY(int y) {

this.y = y;

}

}

public static void main(String[] args) {

// TODO Auto-generated method stub

Dian da = null;

da.setX(1);

System.out.println(da.x);

}

}

Answer 1

da没有初始化，给一个空对象赋值当然会报错Test.Dian da = new Test().new Dian(); da.setX(1);