java之String变量和“==”操作符（1）

先看下面的代码，有助于后面的理解。



Java代码
public class Test  
{  
    public static void main(String[] args)  
    {  
        Test t = new Test();  
        t.show();  
    }  
      
    {  
        System.out.println(1);  
    }  
      
    static 
    {  
        System.out.println(2);  
    }  
      
    public void show()  
    {  
        System.out.println(3);  
    }  
      
    {  
        System.out.println(4);  
    }  
      
    static 
    {  
        System.out.println(5);  
    }  
      
    {  
        System.out.println(6);  
    }  
} 

public class Test
{
public static void main(String[] args)
{
Test t = new Test();
t.show();
}

{
System.out.println(1);
}

static
{
System.out.println(2);
}

public void show()
{
System.out.println(3);
}

{
System.out.println(4);
}

static
{
System.out.println(5);
}

{
System.out.println(6);
}
}

输出为：



Java代码
2 
5 
1 
4 
6 
3 

2
5
1
4
6
3

现在看看下面的这些String变量，用“==”操作符比较它们时会是什么结果呢？如下代码。



Java代码
public class StringTest   
{  
    //11  
    final String fs1 = "H";  
    final String fs2 = "ello";  
    final String fs3 = "Hello";  
    final String fs4 = fs1 + fs2;  
    final String fs5 = "H" + "ello";  
      
    //22  
    final String fs11;  
    final String fs22;  
    final String fs33;  
    final String fs44;  
    final String fs55;  
      
    //static //不能有static  
    {  
        fs11 = "H";  
        fs22 = "ello";  
        fs33 = "Hello";  
        fs44 = fs11 + fs22;  
        fs55 = "H" + "ello";  
    }  
      
    //**********************  
    //**********************  
    //33  
    static String ss1 = "H";  
    static String ss2 = "ello";  
    static String ss3 = "Hello";  
    static String ss4 = ss1 + ss2;  
    static String ss5 = "H" + "ello";  
      
    //44  
    static String ss11;  
    static String ss22;  
    static String ss33;  
    static String ss44;  
    static String ss55;  
      
    static //注释掉也一样  
    {  
        ss11 = "H";  
        ss22 = "ello";  
        ss33 = "Hello";  
        ss44 = ss11 + ss22;  
        ss55 = "H" + "ello";  
    }  
      
    //**********************  
    //**********************  
    //55  
    static final String sfs1 = "H";  
    static final String sfs2 = "ello";  
    static final String sfs3 = "Hello";  
    static final String sfs4 = sfs1 + sfs2;  
    static final String sfs5 = "H" + "ello";  
      
    //66  
    static final String sfs11;  
    static final String sfs22;  
    static final String sfs33;  
    static final String sfs44;  
    static final String sfs55;  
      
    static //不能注释掉  
    {  
        sfs11 = "H";  
        sfs22 = "ello";  
        sfs33 = "Hello";  
        sfs44 = sfs11 + sfs22;  
        sfs55 = "H" + "ello";  
    }  
      
    public static void main(String[] args)  
    {  
        StringTest test = new StringTest();  
          
        test.test1();  
        System.out.println();  
          
        test.test2();  
        System.out.println();  
      
        test.test3();  
        System.out.println();  
          
        test.test4();  
    }  
      
    public void test1()  
    {  
        System.out.println(fs3 == fs4);  
        System.out.println(fs3 == fs5);  
          
        System.out.println(fs3 == fs33);  
        System.out.println(fs3 == fs44);  
        System.out.println(fs3 == fs55);  
          
        System.out.println(fs33 == fs44);  
        System.out.println(fs33 == fs55);  
    }  
      
    public void test2()  
    {  
        System.out.println(ss3 == ss4);  
        System.out.println(ss3 == ss5);  
          
        System.out.println(ss3 == ss33);  
        System.out.println(ss3 == ss44);  
        System.out.println(ss3 == ss55);  
          
        System.out.println(ss33 == ss44);  
        System.out.println(ss33 == ss55);  
    }  
      
    public void test3()  
    {  
        System.out.println(sfs3 == sfs4);  
        System.out.println(sfs3 == sfs5);  
          
        System.out.println(sfs3 == sfs33);  
        System.out.println(sfs3 == sfs44);  
        System.out.println(sfs3 == sfs55);  
          
        System.out.println(sfs33 == sfs44);  
        System.out.println(sfs33 == sfs55);  
    }  
 
    public void test4()  
    {  
        System.out.println(fs3 == ss3);  
        System.out.println(fs3 == ss4);  
        System.out.println(fs3 == ss33);  
        System.out.println(fs3 == ss44);  
        System.out.println(fs3 == sfs4);  
        System.out.println(fs3 == sfs44);  
    }  
} 

public class StringTest
{
//11
final String fs1 = "H";
final String fs2 = "ello";
final String fs3 = "Hello";
final String fs4 = fs1 + fs2;
final String fs5 = "H" + "ello";

//22
final String fs11;
final String fs22;
final String fs33;
final String fs44;
final String fs55;

//static //不能有static
{
fs11 = "H";
fs22 = "ello";
fs33 = "Hello";
fs44 = fs11 + fs22;
fs55 = "H" + "ello";
}

//**********************
//**********************
//33
static String ss1 = "H";
static String ss2 = "ello";
static String ss3 = "Hello";
static String ss4 = ss1 + ss2;
static String ss5 = "H" + "ello";

//44
static String ss11;
static String ss22;
static String ss33;
static String ss44;
static String ss55;

static //注释掉也一样
{
ss11 = "H";
ss22 = "ello";
ss33 = "Hello";
ss44 = ss11 + ss22;
ss55 = "H" + "ello";
}

//**********************
//**********************
//55
static final String sfs1 = "H";
static final String sfs2 = "ello";
static final String sfs3 = "Hello";
static final String sfs4 = sfs1 + sfs2;
static final String sfs5 = "H" + "ello";

//66
static final String sfs11;
static final String sfs22;
static final String sfs33;
static final String sfs44;
static final String sfs55;

static //不能注释掉
{
sfs11 = "H";
sfs22 = "ello";
sfs33 = "Hello";
sfs44 = sfs11 + sfs22;
sfs55 = "H" + "ello";
}

public static void main(String[] args)
{
StringTest test = new StringTest();

test.test1();
System.out.println();

test.test2();
System.out.println();

test.test3();
System.out.println();

test.test4();
}

public void test1()
{
System.out.println(fs3 == fs4);
System.out.println(fs3 == fs5);

System.out.println(fs3 == fs33);
System.out.println(fs3 == fs44);
System.out.println(fs3 == fs55);

System.out.println(fs33 == fs44);
System.out.println(fs33 == fs55);
}

public void test2()
{
System.out.println(ss3 == ss4);
System.out.println(ss3 == ss5);

System.out.println(ss3 == ss33);
System.out.println(ss3 == ss44);
System.out.println(ss3 == ss55);

System.out.println(ss33 == ss44);
System.out.println(ss33 == ss55);
}

public void test3()
{
System.out.println(sfs3 == sfs4);
System.out.println(sfs3 == sfs5);

System.out.println(sfs3 == sfs33);
System.out.println(sfs3 == sfs44);
System.out.println(sfs3 == sfs55);

System.out.println(sfs33 == sfs44);
System.out.println(sfs33 == sfs55);
}

public void test4()
{
System.out.println(fs3 == ss3);
System.out.println(fs3 == ss4);
System.out.println(fs3 == ss33);
System.out.println(fs3 == ss44);
System.out.println(fs3 == sfs4);
System.out.println(fs3 == sfs44);
}
}



输出为：

Java代码
true 
true 
true 
false 
true 
false 
true 
 
false 
true 
true 
false 
true 
false 
true 
 
true 
true 
true 
false 
true 
false 
true 
 
true 
false 
true 
false 
true 
false