java中关于null的案例,null+null会等于什么鬼呢？

女爷i 2022-11-06 04:48 186阅读 0赞

**直接上代码和截图**

![20210308015100717.png][]

package com.test;
    
    public class User {
    	
        private String a;
        
        private int b = 66;
        String city;//引用数据类型的默认值是null
        
        public static void main(String[] args) {
        	User test = new User();
    		System.out.println(test.city);//null
    		String str1 = null;
    		System.out.println(str1);//null
    		System.out.println(str1 + "abc");//nullabc
    		
    		str1 = "null";
    		System.out.println(str1 + "efg");//nullefg
    		System.out.println(str1 + null);//nullnull
    		System.out.println(null + "hello");//nullhello
    		System.out.println(null + "");//null
    		
    		int a = 5;
    //		System.out.println(a == null);//报错,连编译都通不过
    		System.out.println((Integer)0 == null);//false
    //		System.out.println(null + null);//报错,连编译都通不过
    		
    		String n = null;
    		String m = null;
    		System.out.println(n + m);//nullnull
    	}
    }

**运行结果如下：**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2N6aDUwMA_size_16_color_FFFFFF_t_70][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2N6aDUwMA_size_16_color_FFFFFF_t_70 1][]

[20210308015100717.png]: /images/20221023/99ca09340f1e4abfb5e8cee5d5a5b0f5.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2N6aDUwMA_size_16_color_FFFFFF_t_70]: /images/20221023/7dab4317bfff49b7941ae96242dcd3bb.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2N6aDUwMA_size_16_color_FFFFFF_t_70 1]: /images/20221023/f3117b66f9b94162b863f1b831fc3dd3.png