代码:
System.out.println((String)null ==null );
System.out.println((Integer)null==null);
System.out.println(String.valueOf((String)null));
System.out.println(String.valueOf((Integer)null));
System.out.println(String.valueOf(null));
运行截图:
String)null null True (Integer)nullnull True String.valueOf((String)null) “null” String.valueOf((Integer)null) “null” String.valueOf(null) 报错 (String)null,(Integer)null,null用==相比较都是True,String.valueOf(null)报错