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 FilesJavajdk1.7.0_71injava" -Didea.launcher.port=7532 "-Didea.launcher.bin.path=C:Program Files (x86)JetBrainsIntelliJ IDEA 2016.1.3in" -Dfile.encoding=UTF-8 -classpath "C:Program FilesJavajdk1.7.0_71jrelibcharsets.jar;C:Program FilesJavajdk1.7.0_71jrelibdeploy.jar;C:Program FilesJavajdk1.7.0_71jrelibextaccess-bridge-64.jar;C:Program FilesJavajdk1.7.0_71jrelibextdnsns.jar;C:Program FilesJavajdk1.7.0_71jrelibextjaccess.jar;C:Program FilesJavajdk1.7.0_71jrelibextlocaledata.jar;C:Program FilesJavajdk1.7.0_71jrelibextsunec.jar;C:Program FilesJavajdk1.7.0_71jrelibextsunjce_provider.jar;C:Program FilesJavajdk1.7.0_71jrelibextsunmscapi.jar;C:Program FilesJavajdk1.7.0_71jrelibextzipfs.jar;C:Program FilesJavajdk1.7.0_71jrelibjavaws.jar;C:Program FilesJavajdk1.7.0_71jrelibjce.jar;C:Program FilesJavajdk1.7.0_71jrelibjfr.jar;C:Program FilesJavajdk1.7.0_71jrelibjfxrt.jar;C:Program FilesJavajdk1.7.0_71jrelibjsse.jar;C:Program FilesJavajdk1.7.0_71jrelibmanagement-agent.jar;C:Program FilesJavajdk1.7.0_71jrelibplugin.jar;C:Program FilesJavajdk1.7.0_71jrelib esources.jar;C:Program FilesJavajdk1.7.0_71jrelib t.jar;D:workspace_testhello-worldoutproductionhello-world;C:Program Files (x86)JetBrainsIntelliJ IDEA 2016.1.3libidea_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+" _String2 value is : "+_String2); System.out.println("_String1 identityHashCode is :"+System.identityHashCode(_String1)+" _String2 identityHashCode is :"+System.identityHashCode(_String2)); System.out.println("_String1==_String2 is : "+(_String1==_String2)+" "); String _String3 = new String("godtrue"); String _String4 = new String("godtrue"); System.out.println("_String3 value is : "+_String3+" _String4 value is : "+_String4); System.out.println("_String3 identityHashCode is :"+System.identityHashCode(_String3)+" _String4 identityHashCode is :"+System.identityHashCode(_String4)); System.out.println("_String3==_String4 is : "+(_String3==_String4)+" "); String _String5 = _String1; String _String6 = _String1; System.out.println("_String5 value is : "+_String5+" _String6 value is : "+_String6); System.out.println("_String5 identityHashCode is :"+System.identityHashCode(_String5)+" _String6 identityHashCode is :"+System.identityHashCode(_String6)); System.out.println("_String5==_String6 is : "+(_String5==_String6)+" "); String _String7 = _String3; String _String8 = _String3; System.out.println("_String7 value is : "+_String7+" _String8 value is : "+_String8); System.out.println("_String7 identityHashCode is :"+System.identityHashCode(_String7)+" _String8 identityHashCode is :"+System.identityHashCode(_String8)); System.out.println("_String7==_String8 is : "+(_String7==_String8)+" "); String _String9 = _String1; String _String0 = _String3; System.out.println("_String9 value is : "+_String9+" _String0 value is : "+_String0); System.out.println("_String9 identityHashCode is :"+System.identityHashCode(_String9)+" _String0 identityHashCode is :"+System.identityHashCode(_String0)); System.out.println("_String9==_String0 is : "+(_String9==_String0)+" "); } }
上例运行的结果，如下所示（每次运行identityHashCode都不同的哟）：
"C:Program FilesJavajdk1.7.0_71injava" -Didea.launcher.port=7534 "-Didea.launcher.bin.path=C:Program Files (x86)JetBrainsIntelliJ IDEA 2016.1.3in" -Dfile.encoding=UTF-8 -classpath "C:Program FilesJavajdk1.7.0_71jrelibcharsets.jar;C:Program FilesJavajdk1.7.0_71jrelibdeploy.jar;C:Program FilesJavajdk1.7.0_71jrelibextaccess-bridge-64.jar;C:Program FilesJavajdk1.7.0_71jrelibextdnsns.jar;C:Program FilesJavajdk1.7.0_71jrelibextjaccess.jar;C:Program FilesJavajdk1.7.0_71jrelibextlocaledata.jar;C:Program FilesJavajdk1.7.0_71jrelibextsunec.jar;C:Program FilesJavajdk1.7.0_71jrelibextsunjce_provider.jar;C:Program FilesJavajdk1.7.0_71jrelibextsunmscapi.jar;C:Program FilesJavajdk1.7.0_71jrelibextzipfs.jar;C:Program FilesJavajdk1.7.0_71jrelibjavaws.jar;C:Program FilesJavajdk1.7.0_71jrelibjce.jar;C:Program FilesJavajdk1.7.0_71jrelibjfr.jar;C:Program FilesJavajdk1.7.0_71jrelibjfxrt.jar;C:Program FilesJavajdk1.7.0_71jrelibjsse.jar;C:Program FilesJavajdk1.7.0_71jrelibmanagement-agent.jar;C:Program FilesJavajdk1.7.0_71jrelibplugin.jar;C:Program FilesJavajdk1.7.0_71jrelib esources.jar;C:Program FilesJavajdk1.7.0_71jrelib t.jar;D:workspace_testhello-worldoutproductionhello-world;C:Program Files (x86)JetBrainsIntelliJ IDEA 2016.1.3libidea_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+" int2 value is : "+int2); System.out.println("int1 identityHashCode is :"+System.identityHashCode(int1)+" int2 identityHashCode is :"+System.identityHashCode(int2)); System.out.println("int1==int2 is : "+(int1==int2)+" "); Integer _Integer1 = 9; Integer _Integer2 = 9; System.out.println("_Integer1 value is : "+_Integer1+" _Integer2 value is : "+_Integer2); System.out.println("_Integer1 identityHashCode is :"+System.identityHashCode(_Integer1)+" _Integer2 identityHashCode is :"+System.identityHashCode(_Integer2)); System.out.println("_Integer1==_Integer2 is : "+(_Integer1==_Integer2)+" "); Integer _Integer3 = new Integer(9); Integer _Integer4 = new Integer(9); System.out.println("_Integer3 value is : "+_Integer3+" _Integer4 value is : "+_Integer4); System.out.println("_Integer3 identityHashCode is :"+System.identityHashCode(_Integer3)+" _Integer4 identityHashCode is :"+System.identityHashCode(_Integer4)); System.out.println("_Integer3==_Integer4 is : "+(_Integer3==_Integer4)+" "); Integer _Integer5 = int1; Integer _Integer6 = int1; System.out.println("_Integer5 value is : "+_Integer5+" _Integer6 value is : "+_Integer6); System.out.println("_Integer5 identityHashCode is :"+System.identityHashCode(_Integer5)+" _Integer6 identityHashCode is :"+System.identityHashCode(_Integer6)); System.out.println("_Integer5==_Integer6 is : "+(_Integer5==_Integer6)+" "); Integer _Integer7 = _Integer1; Integer _Integer8 = _Integer1; System.out.println("_Integer7 value is : "+_Integer7+" _Integer8 value is : "+_Integer8); System.out.println("_Integer7 identityHashCode is :"+System.identityHashCode(_Integer7)+" _Integer8 identityHashCode is :"+System.identityHashCode(_Integer8)); System.out.println("_Integer7==_Integer8 is : "+(_Integer7==_Integer8)+" "); Integer _Integer9 = _Integer3; Integer _Integer0 = _Integer3; System.out.println("_Integer9 value is : "+_Integer9+" _Integer0 value is : "+_Integer0); System.out.println("_Integer9 identityHashCode is :"+System.identityHashCode(_Integer9)+" _Integer0 identityHashCode is :"+System.identityHashCode(_Integer0)); System.out.println("_Integer9==_Integer0 is : "+(_Integer9==_Integer0)+" "); } }
上例运行的结果，如下所示（每次运行identityHashCode都不同的哟）：
"C:Program FilesJavajdk1.7.0_71injava" -Didea.launcher.port=7536 "-Didea.launcher.bin.path=C:Program Files (x86)JetBrainsIntelliJ IDEA 2016.1.3in" -Dfile.encoding=UTF-8 -classpath "C:Program FilesJavajdk1.7.0_71jrelibcharsets.jar;C:Program FilesJavajdk1.7.0_71jrelibdeploy.jar;C:Program FilesJavajdk1.7.0_71jrelibextaccess-bridge-64.jar;C:Program FilesJavajdk1.7.0_71jrelibextdnsns.jar;C:Program FilesJavajdk1.7.0_71jrelibextjaccess.jar;C:Program FilesJavajdk1.7.0_71jrelibextlocaledata.jar;C:Program FilesJavajdk1.7.0_71jrelibextsunec.jar;C:Program FilesJavajdk1.7.0_71jrelibextsunjce_provider.jar;C:Program FilesJavajdk1.7.0_71jrelibextsunmscapi.jar;C:Program FilesJavajdk1.7.0_71jrelibextzipfs.jar;C:Program FilesJavajdk1.7.0_71jrelibjavaws.jar;C:Program FilesJavajdk1.7.0_71jrelibjce.jar;C:Program FilesJavajdk1.7.0_71jrelibjfr.jar;C:Program FilesJavajdk1.7.0_71jrelibjfxrt.jar;C:Program FilesJavajdk1.7.0_71jrelibjsse.jar;C:Program FilesJavajdk1.7.0_71jrelibmanagement-agent.jar;C:Program FilesJavajdk1.7.0_71jrelibplugin.jar;C:Program FilesJavajdk1.7.0_71jrelib esources.jar;C:Program FilesJavajdk1.7.0_71jrelib t.jar;D:workspace_testhello-worldoutproductionhello-world;C:Program Files (x86)JetBrainsIntelliJ IDEA 2016.1.3libidea_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）