JAVA equals和==的区别

一句话：

==比较的是内存地址，如果内存地址相同，则相同；

equals 内存地址相同则相同，如果内存地址不相同，看子类equals重写方法的具体实现。

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package JavaCoreTechDemo.base;   import sun.misc.Unsafe;   import java.lang.reflect.Field;   /**  * Created by IntelliJ IDEA.  * User: zz  * Date: 2015/5/10  */ public class JavaEqualsAndDoubleEqual {     public static void main(String[] args) throws Exception {         testInt();         testNotOverrideEquals();         testStringEquals();         testNewStringEquals();     }       private static void testInt() {         System.out.println("=====================testInt=========================");         int a = 1;         int b = 1;         System.out.println(String.format("a mem addr=%s,b mem addr=%s", AddressPrint.addressOf(a), AddressPrint.addressOf(b)));         if (a == b) {             System.out.println("a==b");         }         Integer c = new Integer(a);         Integer d = new Integer(b);         System.out.println(String.format("c mem addr=%s,d mem addr=%s", AddressPrint.addressOf(c), AddressPrint.addressOf(d)));           if (c == d) {             System.out.println("Integer  c  == Integer  d");         }         System.out.println("this.value=" + c.intValue());         System.out.println("(Integer)var1=" + (Integer) d);           if (c.equals(d)) {             System.out.println("Integer  c  equals Integer  d");         }       }       private static void testNotOverrideEquals() {         System.out.println("=====================testNotOverrideEquals=========================");         TestA testA1 = new TestA();         TestA testA2 = new TestA();         System.out.println(String.format("testA1 mem addr=%s,testA2 mem addr=%s", AddressPrint.addressOf(testA1), AddressPrint.addressOf(testA2)));         if (testA1 == testA2) {             System.out.println("TestA testA1  == TestA testA2");         } else {             System.out.println("TestA testA1 != testA2");         }           if (testA1.equals(testA2)) {             //默认实现的equals比较的是对象的内存地址             System.out.println("TestA testA1  equals testA2");         } else {             System.out.println("TestA testA1 not equals testA2");         }     }       private static void testStringEquals() {         System.out.println("=====================testStringEquals=========================");         String s1 = "Monday";         String s2 = "Monday";         System.out.println(String.format("s1 mem addr=%s,s2 mem addr=%s", AddressPrint.addressOf(s1), AddressPrint.addressOf(s2)));         //==比较的是内存地址，s1和s2内存地址一样         if (s1 == s2) {             System.out.println("s1 == s2");         } else {             System.out.println("s1 != s2");         }         if (s1.equals(s2)) {             System.out.println("s1 equals s2");         } else {             System.out.println("s1 not equals s2");         }     }       private static void testNewStringEquals() {         System.out.println("=====================testNewStringEquals=========================");         String s1 = "Monday";         String s2 = new String("Monday");         //==比较的是内存地址，s1和s2内存地址不一样         System.out.println(String.format("s1 mem addr=%s,s2 mem addr=%s", AddressPrint.addressOf(s1), AddressPrint.addressOf(s2)));           if (s1 == s2) {             System.out.println("s1 == s2");         } else {             System.out.println("s1 != s2");         }         //String类重写了equals，比较的是每个字符         if (s1.equals(s2)) {             System.out.println("s1 equals s2");         } else {             System.out.println("s1 not equals s2");         }     } }   class TestA {   }   class AddressPrint {     private static Unsafe unsafe;       static {         try {             Field field = Unsafe.class.getDeclaredField("theUnsafe");             field.setAccessible(true);             unsafe = (Unsafe) field.get(null);         } catch (Exception e) {             e.printStackTrace();         }     }       public static String addressOf(Object o) {         Object[] array = new Object[]{o};           long baseOffset = unsafe.arrayBaseOffset(Object[].class);         int addressSize = unsafe.addressSize();         try {               long objectAddress;             switch (addressSize) {                 case 4:                     objectAddress = unsafe.getInt(array, baseOffset);                     break;                 case 8:                     objectAddress = unsafe.getLong(array, baseOffset);                     break;                 default:                     throw new Error("unsupported address size: " + addressSize);             }               return (Long.toHexString(objectAddress));         } catch (Exception e) {             System.out.println("unsupported address size:" + addressSize);             return null;         }     }   }