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javaÖÐ== ÓëequalsµÄÇø±ð

public class test1
{
 public static void main(String[] args){
  //== ÓëequalsµÄÇø±ð
  //1.nullµÄ±È½Ï£ºÖ»ÄÜÓÃ==
  System.out.println("1.nullµÄ±È½Ï£ºÖ»ÄÜÓÃ==");
  Object o1=null,o2=null;
  System.out.println(null==null&&o1==null&&o1==o2);//true
        //System.out.println(o1.equals(o2)) //Å׳öÒì³£
         
  //2.»ù±¾ÀàÐ͵ıȽϣºÖ»ÄÜÓÃ==
  System.out.println("\n\n2.»ù±¾ÀàÐ͵ıȽϣºÖ»ÄÜÓÃ==");
  double i=2.4,j=2.4;
  System.out.println(i==j);//true
  
  
  //3.ÒýÓõıȽϣºµ±×ÓÀàÖØÐ´¹ýequalsÖ®ºó£¬ ==ÓëequalsµÄ±È½ÏЧ¹û²¢²»Í¬£¬e.g  String
  //==Ï൱ÓÚ×îԭʼµÄequals
  /*¸ùÀàObjectÓÐÈçÏ´úÂë
   * public boolean equals(Object obj) {
   * return (this == obj);
      * }
   * */
  System.out.println("\n\n3.ÒýÓõıȽϣº" +
    "µ±×ÓÀàÖØÐ´¹ýequalsÖ®ºó£¬ ==ÓëequalsµÄ±È½ÏЧ¹û²¢²»Í¬£¬e.g  String");
  String str1=new String("string"),str2=new String("string"),str3=str1;
  System.out.println(str3==str1&&str3.equals(str1));//Ö¸Ïòͬһ¶ÔÏó£¬true
  System.out.println(str1==str2);//²¢²»Ö¸Ïòͬһ¸ö¶ÔÏó£¬false
  System.out.println(str1.equals(str2));//ÓÉÓÚequals±»ÖØÐ´ÁË£¬
  //Ö»±È½Ï ËûÃǵÄÖµ£¬ËùÒÔ±¾Àý·µ»Øtrue
  
  //4.×¢ÒâµÄµØ·½,new String() ÓëÖØÔØ·ûºÅ=µÄÇø±ð
  System.out.println("\n\n4.×¢ÒâµÄµØ·½,new String() ÓëÖØÔØ·ûºÅ=µÄÇø±ð");
  System.out.println("string"=="string");//·µ»Øtrue,˵Ã÷Ö¸ÏòµÄÊÇͬһ¸ö¶ÔÏó
  System.out.println(new String("string")=="string");//·µ»Øfalse
  
  
 }
}


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