Java中equals()与==操作符
一般来说equals()方法是比较两个对象值的。
例如比较两个Integer 对象
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedBloc
kStart.gif) ![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/
ContractedBlock.gif) public class Equalival … {
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedSubB
lockStart.gif) ![](http://images.csdn.net/syntaxhighlighting/OutliningIndicato
rs/ContractedSubBlock.gif) public static void main(String[] args) … {
Integer n1 = new Integer( 47 );
Integer n2 = new Integer( 47 );
System.out.println(n1.equals(n2));
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedSubB
lockEnd.gif) }
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedBloc
kEnd.gif) }
打印true
//Thinking in Java中的例子
==操作符是用来比较引用是否相等
public class Equalival
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedBloc
kStart.gif) ![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/
ContractedBlock.gif) … {
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedSubB
lockStart.gif) ![](http://images.csdn.net/syntaxhighlighting/OutliningIndicato
rs/ContractedSubBlock.gif) public static void main(String[] args) … {
Integer n1 = new Integer( 47 );
Integer n2 = new Integer( 47 );
System.out.println(n1 == n2);
System.out.println(n1 != n2);
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedSubB
lockEnd.gif) }
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedBloc
kEnd.gif) }
打印false,true
感觉以上的例子并没有说明什么看看下面的这个String的例子:
public class TestRef
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedBloc
kStart.gif) ![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/
ContractedBlock.gif) … {
public static void main(String[] args)
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedSubB
lockStart.gif) ![](http://images.csdn.net/syntaxhighlighting/OutliningIndicato
rs/ContractedSubBlock.gif) … {
String s = new String( " a " );
if (s == " a " )
System.out.println( " true1 " );
if (s.equals( " a " ))
System.out.println( " true2 " );
String ss = " a " ;
if (ss == " a " )
System.out.println( " true3 " );
if (ss.equals( " a " ))
System.out.println( " true4 " );
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedSubB
lockEnd.gif) }
![](http://images.csdn.net/syntaxhighlighting/OutliningIndicators/ExpandedBloc
kEnd.gif) }
这个打印true2,true3,true4。因为new String时在堆中生成了空间给“a”,对于第一次的s==“a”时,栈分配空间给"a",并把"a"当
成一个匿名的对象。赋值ss=“a”,意味着在栈中分配了空间给"a",并把"a"这个匿名的对象引用赋给ss。,所以s与"a"的引用不等。而"a"再次出现在代码
中时,编译器查找到先前的“a”对象,而不是再分配内存给"a"。所以ss与"a"的引用是相等的。但不管引用是否相等,其值都是"a",这便看出了equals()
的威力。