java.lang中String"="和"equals()"函数解析

　　java.lang是java语言的基础包。String类为lang包中的一个基础类。本文主要讨论 "="和"equals()"方法对String的不同判断结果。

"=" .VS. "equals()" :

　　"="判断的是两个String类型的引用是否指向同一个对象，如果是，那么表达式结果为true，如果不是，那么表达式结果为false;

　　"equals"判断的是两个String类型的引用所指向对象的值，如果相等，那么返回结果为true，如果不相等，那么返回结果为false;

下面是我的一段简单的实验程序。

package BasicKnowledge.Testlang;

public class StringTest {
    public static void main(String args[])
    {
        String str1;
        str1 = new String("Str");
        String str2 = new String("Str");
        
        
        
        String str3;
        str3 = str1;
        String equal = "The two strings are equal with";
        String notEqual = "The two strings are not equal";
        
        String stat2 = "str1 and str2 are two different objects but they have the same value";
        if(equalSign(str1,str2))
        {
            System.out.println(stat2+";"+equal+" '=' sign");
        }else System.out.println(stat2+";"+notEqual+" '=' sign");
        
        if(equalFunction(str1,str2))
        {
            System.out.println(stat2+";"+equal+ " 'equal()' function");
        }else System.out.println(stat2+";"+notEqual+" 'equal()' fuction");
        
        str3 = str1;
        String stat = "str3 shares the same reference with str1";
        
        if(equalSign(str1,str3))
        {
            System.out.println(stat+";"+equal+" '=' sign");
        }else System.out.println(stat+";"+notEqual+" '=' sign");
        
        if(equalFunction(str1,str3))
        {
            System.out.println(stat+";"+equal+ " 'equal()' function");
        }else System.out.println(stat+";"+notEqual+" 'equal()' fuction");
    }
    
    static  boolean equalSign(String a, String b)//在静态方法中,是不能访问非静态成员,所以这里用static来形容
    {
        boolean backValue = true;
        if(a == b)
        {
            backValue = true;
        }else backValue = false;
        return backValue;
    }
    
    static  boolean equalFunction(String a, String b)
    {
        boolean backValue = true;
        if(a.equals(b))
        {
            backValue = true;
        }else backValue = false;
        return backValue;
    }

}

编译和运行结果如下：

str1 and str2 are two different objects but they have the same value;The two strings are not equal '=' sign
str1 and str2 are two different objects but they have the same value;The two strings are equal with 'equal()' function
str3 shares the same reference with str1;The two strings are equal with '=' sign
str3 shares the same reference with str1;The two strings are equal with 'equal()' function