//????????這里有個要注意的
????????String?v1?=?"123456";
????????String?v2?=?"123456";
????????System.out.println(v1?==?v2);
????????System.out.println(v1?==?"123456");
????????System.out.println(v2?==?"123456");
????????System.out.println(v1.equals("123456"));

這樣就可以?

String?fileName?=?"HelloWorld.java";
int?index?=?fileName.indexOf('.');

String?prefix?=?fileName.substring(index+1);
System.out.println(prefix);
System.out.println(prefix?==?"java");??//為啥他就是??false?了?很神奇啊