从Java源码看String的两种比较方式

 1 public class EqualsDemo {
 2 
 3     /**
 4      * @param args
 5      */
 6     public static void main(String[] args) {
 7         String s1 = "String";
 8         String s2 = "String";
 9         String s3 = new String("String");
10         String s4 = new String("String");
11         System.out.println(s1 == s2);
12         System.out.println(s1 == s3);
13         System.out.println(s3 == s4);
14     }
15 }

 1 public class EqualsDemo {
 2 
 3     /**
 4      * @param args
 5      */
 6     public static void main(String[] args) {
 7         String s1 = "String";
 8         String s2 = "String";
 9         String s3 = new String("String");
10         String s4 = new String("String");
11         System.out.println(s1.equals(s2));
12         System.out.println(s1.equals(s3));
13         System.out.println(s3.equals(s1));
14         System.out.println(s3.equals(s4));
15     }
16 }

 1   /**
 2      * Compares this string to the specified object.  The result is {@code
 3      * true} if and only if the argument is not {@code null} and is a {@code
 4      * String} object that represents the same sequence of characters as this
 5      * object.
 6      *
 7      * @param  anObject
 8      *         The object to compare this {@code String} against
 9      *
10      * @return  {@code true} if the given object represents a {@code String}
11      *          equivalent to this string, {@code false} otherwise
12      *
13      * @see  #compareTo(String)
14      * @see  #equalsIgnoreCase(String)
15      */
16     public boolean equals(Object anObject) {
17         if (this == anObject) {
18             return true;
19         }
20         if (anObject instanceof String) {
21             String anotherString = (String)anObject;
22             int n = value.length;
23             if (n == anotherString.value.length) {
24                 char v1[] = value;
25                 char v2[] = anotherString.value;
26                 int i = 0;
27                 while (n-- != 0) {
28                     if (v1[i] != v2[i])
29                         return false;
30                     i++;
31                 }
32                 return true;
33             }
34         }
35         return false;
36     }