==和equals的简单比较
前言：==和equals这个两个东西，经常放在一块做比较，下面我也给出一个简单的例子，对他俩进行一个简单的比较，先看例子，然后在看结论。（实验环境：win7+jdk7）
1：==和equals简单比较的实例代码如下
public class BooleanTestMain {
public static void main(String [] args){
Boolean _Boolean1 = true;
Boolean _Boolean2 = true;
Boolean _Boolean3 = new Boolean(true);
Boolean _Boolean4 = new Boolean(true);
//输入对象的hashCode和identityHashCode，当对应的类没有重写hashCode()方法时，hashCode和identityHashCode是一致的
System.out.println("_Boolean1.hashCode() is : "+_Boolean1.hashCode()+" System.identityHashCode(_Boolean1) is : "+ System.identityHashCode(_Boolean1));
System.out.println("_Boolean2.hashCode() is : "+_Boolean2.hashCode()+" System.identityHashCode(_Boolean2) is : "+ System.identityHashCode(_Boolean2));
System.out.println("_Boolean3.hashCode() is : "+_Boolean3.hashCode()+" System.identityHashCode(_Boolean3) is : "+ System.identityHashCode(_Boolean3));
System.out.println("_Boolean4.hashCode() is : "+_Boolean4.hashCode()+" System.identityHashCode(_Boolean4) is : "+ System.identityHashCode(_Boolean4));
//==比较的是对象引用地址值
System.out.println("_Boolean1==_Boolean2 is : "+(_Boolean1==_Boolean2));
System.out.println("_Boolean3==_Boolean4 is : "+(_Boolean3==_Boolean4));
System.out.println("_Boolean1==_Boolean3 is : "+(_Boolean1==_Boolean3));
//equals比较的是对象的值，如果对象没有重写equals的话，其作用和==一样，因为Object类的equals也是通过==来比较的
System.out.println("_Boolean1.equals(_Boolean2) is : "+(_Boolean1.equals(_Boolean2)));
System.out.println("_Boolean3.equals(_Boolean4) is : "+(_Boolean3.equals(_Boolean4)));
System.out.println("_Boolean1.equals(_Boolean3) is : "+(_Boolean1.equals(_Boolean3)));
}
}
上例运行的结果如下：
"C:\Program Files\Java\jdk1.7.0_71\bin\java" -Didea.launcher.port=7532 "-Didea.launcher.bin.path=C:\Program Files (x86)\JetBrains\IntelliJ IDEA 2016.1.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.7.0_71\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jce.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jfxrt.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\resources.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\rt.jar;D:\workspace_test\hello-world\out\production\hello-world;C:\Program Files (x86)\JetBrains\IntelliJ IDEA 2016.1.3\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain com.jd.test.equ.BooleanTestMain
_Boolean1.hashCode() is : 1231 System.identityHashCode(_Boolean1) is : 1969344019
_Boolean2.hashCode() is : 1231 System.identityHashCode(_Boolean2) is : 1969344019
_Boolean3.hashCode() is : 1231 System.identityHashCode(_Boolean3) is : 1746959769
_Boolean4.hashCode() is : 1231 System.identityHashCode(_Boolean4) is : 756415799
_Boolean1==_Boolean2 is : true
_Boolean3==_Boolean4 is : false
_Boolean1==_Boolean3 is : false
_Boolean1.equals(_Boolean2) is : true
_Boolean3.equals(_Boolean4) is : true
_Boolean1.equals(_Boolean3) is : true Process finished with exit code 0
2：Boolean类的部分源码如下所示，重写了Object的hashCode()和equals()方法
/**
* Returns a hash code for this {@code Boolean} object.
*
* @return the integer {@code 1231} if this object represents
* {@code true}; returns the integer {@code 1237} if this
* object represents {@code false}.
*/
public int hashCode() {
return value ? 1231 : 1237;
} /**
* Returns {@code true} if and only if the argument is not
* {@code null} and is a {@code Boolean} object that
* represents the same {@code boolean} value as this object.
*
* @param obj the object to compare with.
* @return {@code true} if the Boolean objects represent the
* same value; {@code false} otherwise.
*/
public boolean equals(Object obj) {
if (obj instanceof Boolean) {
return value == ((Boolean)obj).booleanValue();
}
return false;
}
3：Object类的equals()方法的源码如下所示，也是通过==来比较的
/**
* Indicates whether some other object is "equal to" this one.
* <p>
* The {@code equals} method implements an equivalence relation
* on non-null object references:
* <ul>
* <li>It is <i>reflexive</i>: for any non-null reference value
* {@code x}, {@code x.equals(x)} should return
* {@code true}.
* <li>It is <i>symmetric</i>: for any non-null reference values
* {@code x} and {@code y}, {@code x.equals(y)}
* should return {@code true} if and only if
* {@code y.equals(x)} returns {@code true}.
* <li>It is <i>transitive</i>: for any non-null reference values
* {@code x}, {@code y}, and {@code z}, if
* {@code x.equals(y)} returns {@code true} and
* {@code y.equals(z)} returns {@code true}, then
* {@code x.equals(z)} should return {@code true}.
* <li>It is <i>consistent</i>: for any non-null reference values
* {@code x} and {@code y}, multiple invocations of
* {@code x.equals(y)} consistently return {@code true}
* or consistently return {@code false}, provided no
* information used in {@code equals} comparisons on the
* objects is modified.
* <li>For any non-null reference value {@code x},
* {@code x.equals(null)} should return {@code false}.
* </ul>
* <p>
* The {@code equals} method for class {@code Object} implements
* the most discriminating possible equivalence relation on objects;
* that is, for any non-null reference values {@code x} and
* {@code y}, this method returns {@code true} if and only
* if {@code x} and {@code y} refer to the same object
* ({@code x == y} has the value {@code true}).
* <p>
* Note that it is generally necessary to override the {@code hashCode}
* method whenever this method is overridden, so as to maintain the
* general contract for the {@code hashCode} method, which states
* that equal objects must have equal hash codes.
*
* @param obj the reference object with which to compare.
* @return {@code true} if this object is the same as the obj
* argument; {@code false} otherwise.
* @see #hashCode()
* @see java.util.HashMap
*/
public boolean equals(Object obj) {
return (this == obj);
}
4：为了认清==比较的本质，我又多实验了一把，如下所示
public class EquStringTestMain {
public static void main(String[]args){
String _String1 = "godtrue";
String _String2 = "godtrue";
System.out.println("_String1 value is : "+_String1+"\n_String2 value is : "+_String2);
System.out.println("_String1 identityHashCode is :"+System.identityHashCode(_String1)+"\n_String2 identityHashCode is :"+System.identityHashCode(_String2));
System.out.println("_String1==_String2 is : "+(_String1==_String2)+"\n");
String _String3 = new String("godtrue");
String _String4 = new String("godtrue");
System.out.println("_String3 value is : "+_String3+"\n_String4 value is : "+_String4);
System.out.println("_String3 identityHashCode is :"+System.identityHashCode(_String3)+"\n_String4 identityHashCode is :"+System.identityHashCode(_String4));
System.out.println("_String3==_String4 is : "+(_String3==_String4)+"\n");
String _String5 = _String1;
String _String6 = _String1;
System.out.println("_String5 value is : "+_String5+"\n_String6 value is : "+_String6);
System.out.println("_String5 identityHashCode is :"+System.identityHashCode(_String5)+"\n_String6 identityHashCode is :"+System.identityHashCode(_String6));
System.out.println("_String5==_String6 is : "+(_String5==_String6)+"\n");
String _String7 = _String3;
String _String8 = _String3;
System.out.println("_String7 value is : "+_String7+"\n_String8 value is : "+_String8);
System.out.println("_String7 identityHashCode is :"+System.identityHashCode(_String7)+"\n_String8 identityHashCode is :"+System.identityHashCode(_String8));
System.out.println("_String7==_String8 is : "+(_String7==_String8)+"\n");
String _String9 = _String1;
String _String0 = _String3;
System.out.println("_String9 value is : "+_String9+"\n_String0 value is : "+_String0);
System.out.println("_String9 identityHashCode is :"+System.identityHashCode(_String9)+"\n_String0 identityHashCode is :"+System.identityHashCode(_String0));
System.out.println("_String9==_String0 is : "+(_String9==_String0)+"\n");
}
}
上例运行的结果，如下所示（每次运行identityHashCode都不同的哟）：
"C:\Program Files\Java\jdk1.7.0_71\bin\java" -Didea.launcher.port=7534 "-Didea.launcher.bin.path=C:\Program Files (x86)\JetBrains\IntelliJ IDEA 2016.1.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.7.0_71\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jce.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jfxrt.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\resources.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\rt.jar;D:\workspace_test\hello-world\out\production\hello-world;C:\Program Files (x86)\JetBrains\IntelliJ IDEA 2016.1.3\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain com.jd.test.equ.EquStringTestMain
_String1 value is : godtrue
_String2 value is : godtrue
_String1 identityHashCode is :1748462787
_String2 identityHashCode is :1748462787
_String1==_String2 is : true _String3 value is : godtrue
_String4 value is : godtrue
_String3 identityHashCode is :247835561
_String4 identityHashCode is :1401482194
_String3==_String4 is : false _String5 value is : godtrue
_String6 value is : godtrue
_String5 identityHashCode is :1748462787
_String6 identityHashCode is :1748462787
_String5==_String6 is : true _String7 value is : godtrue
_String8 value is : godtrue
_String7 identityHashCode is :247835561
_String8 identityHashCode is :247835561
_String7==_String8 is : true _String9 value is : godtrue
_String0 value is : godtrue
_String9 identityHashCode is :1748462787
_String0 identityHashCode is :247835561
_String9==_String0 is : false
5：String类相对特殊一点，再来一个栗子尝尝
public class EquTestMain {
public static void main(String[]args){
int int1 = 9;
int int2 = 9;
System.out.println("int1 value is : "+int1+"\nint2 value is : "+int2);
System.out.println("int1 identityHashCode is :"+System.identityHashCode(int1)+"\nint2 identityHashCode is :"+System.identityHashCode(int2));
System.out.println("int1==int2 is : "+(int1==int2)+"\n");
Integer _Integer1 = 9;
Integer _Integer2 = 9;
System.out.println("_Integer1 value is : "+_Integer1+"\n_Integer2 value is : "+_Integer2);
System.out.println("_Integer1 identityHashCode is :"+System.identityHashCode(_Integer1)+"\n_Integer2 identityHashCode is :"+System.identityHashCode(_Integer2));
System.out.println("_Integer1==_Integer2 is : "+(_Integer1==_Integer2)+"\n");
Integer _Integer3 = new Integer(9);
Integer _Integer4 = new Integer(9);
System.out.println("_Integer3 value is : "+_Integer3+"\n_Integer4 value is : "+_Integer4);
System.out.println("_Integer3 identityHashCode is :"+System.identityHashCode(_Integer3)+"\n_Integer4 identityHashCode is :"+System.identityHashCode(_Integer4));
System.out.println("_Integer3==_Integer4 is : "+(_Integer3==_Integer4)+"\n");
Integer _Integer5 = int1;
Integer _Integer6 = int1;
System.out.println("_Integer5 value is : "+_Integer5+"\n_Integer6 value is : "+_Integer6);
System.out.println("_Integer5 identityHashCode is :"+System.identityHashCode(_Integer5)+"\n_Integer6 identityHashCode is :"+System.identityHashCode(_Integer6));
System.out.println("_Integer5==_Integer6 is : "+(_Integer5==_Integer6)+"\n");
Integer _Integer7 = _Integer1;
Integer _Integer8 = _Integer1;
System.out.println("_Integer7 value is : "+_Integer7+"\n_Integer8 value is : "+_Integer8);
System.out.println("_Integer7 identityHashCode is :"+System.identityHashCode(_Integer7)+"\n_Integer8 identityHashCode is :"+System.identityHashCode(_Integer8));
System.out.println("_Integer7==_Integer8 is : "+(_Integer7==_Integer8)+"\n");
Integer _Integer9 = _Integer3;
Integer _Integer0 = _Integer3;
System.out.println("_Integer9 value is : "+_Integer9+"\n_Integer0 value is : "+_Integer0);
System.out.println("_Integer9 identityHashCode is :"+System.identityHashCode(_Integer9)+"\n_Integer0 identityHashCode is :"+System.identityHashCode(_Integer0));
System.out.println("_Integer9==_Integer0 is : "+(_Integer9==_Integer0)+"\n");
}
}
上例运行的结果，如下所示（每次运行identityHashCode都不同的哟）：
"C:\Program Files\Java\jdk1.7.0_71\bin\java" -Didea.launcher.port=7536 "-Didea.launcher.bin.path=C:\Program Files (x86)\JetBrains\IntelliJ IDEA 2016.1.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.7.0_71\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jce.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jfxrt.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\resources.jar;C:\Program Files\Java\jdk1.7.0_71\jre\lib\rt.jar;D:\workspace_test\hello-world\out\production\hello-world;C:\Program Files (x86)\JetBrains\IntelliJ IDEA 2016.1.3\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain com.jd.test.equ.EquTestMain
int1 value is : 9
int2 value is : 9
int1 identityHashCode is :1401482194
int2 identityHashCode is :1401482194
int1==int2 is : true _Integer1 value is : 9
_Integer2 value is : 9
_Integer1 identityHashCode is :1401482194
_Integer2 identityHashCode is :1401482194
_Integer1==_Integer2 is : true _Integer3 value is : 9
_Integer4 value is : 9
_Integer3 identityHashCode is :1110594262
_Integer4 identityHashCode is :1977385357
_Integer3==_Integer4 is : false _Integer5 value is : 9
_Integer6 value is : 9
_Integer5 identityHashCode is :1401482194
_Integer6 identityHashCode is :1401482194
_Integer5==_Integer6 is : true _Integer7 value is : 9
_Integer8 value is : 9
_Integer7 identityHashCode is :1401482194
_Integer8 identityHashCode is :1401482194
_Integer7==_Integer8 is : true _Integer9 value is : 9
_Integer0 value is : 9
_Integer9 identityHashCode is :1110594262
_Integer0 identityHashCode is :1110594262
_Integer9==_Integer0 is : true
6：如上的代码，如果看完了，也理解了，基本上结论也出来了。（建议先看下hashCode和identityHashCode 的关系）
6-1：==是比较运算符，当是基本数据类型时，比较的是变量的值，当是其他类型的对象时，用它比较的是两个对象的引用地址值是否相等
6-2：equals是一个方法，如果对应的类没有重现Object类的equals()方法，则和==是一样的作用
6-3：identityHashCode更能间接的代表一个对象的引用地址值
6-4：如果一个类没有重写Object类的hashCode方法那么hashCode和identityHashCode是一致的
6-5：hashCode相等时使用==比较，不一定是true
6-6：identityHashCode相等时使用==比较，一定是true
6-7：hashCode相等时使用equals比较，也不一定是true（通常可认为是true，我们自己可以随便定义的）
6-8：我们通常关心的是对象值是否相当（一个值或者多个值），所以对象之间的比较一定要使用equals方法，而非==
7：参看博文如下（观点一致，只是解释的思路或者栗子不同）
Java ==和equals()的区别【详细版】
Java中equals和==的区别
What is the difference between == vs equals() in Java?
java：String使用equals和==比较的区别
java中equals和==的区别
浅谈Java中的equals和==
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