hashCode与equals

 1 /**
 2      * Returns a hash code for this string. The hash code for a
 3      * <code>String</code> object is computed as
 4      * <blockquote><pre>
 5      * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
 6      * </pre></blockquote>
 7      * using <code>int</code> arithmetic, where <code>s[i]</code> is the
 8      * <i>i</i>th character of the string, <code>n</code> is the length of
 9      * the string, and <code>^</code> indicates exponentiation.
10      * (The hash value of the empty string is zero.)
11      *
12      * @return  a hash code value for this object.
13      */
14     public int hashCode() {
15         int h = hash;
16         if (h == 0 && value.length > 0) {
17             char val[] = value;
18 
19             for (int i = 0; i < value.length; i++) {
20                 h = 31 * h + val[i];
21             }
22             hash = h;
23         }
24         return h;
25     }

 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     }

 1     /**
 2      * Associates the specified value with the specified key in this map.
 3      * If the map previously contained a mapping for the key, the old
 4      * value is replaced.
 5      *
 6      * @param key key with which the specified value is to be associated
 7      * @param value value to be associated with the specified key
 8      * @return the previous value associated with <tt>key</tt>, or
 9      *         <tt>null</tt> if there was no mapping for <tt>key</tt>.
10      *         (A <tt>null</tt> return can also indicate that the map
11      *         previously associated <tt>null</tt> with <tt>key</tt>.)
12      */
13     public V put(K key, V value) {
14         if (table == EMPTY_TABLE) {
15             inflateTable(threshold);
16         }
17         if (key == null)
18             return putForNullKey(value);
19         int hash = hash(key);
20         int i = indexFor(hash, table.length);
21         for (Entry<K,V> e = table[i]; e != null; e = e.next) {
22             Object k;
23             if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
24                 V oldValue = e.value;
25                 e.value = value;
26                 e.recordAccess(this);
27                 return oldValue;
28             }
29         }
30 
31         modCount++;
32         addEntry(hash, key, value, i);
33         return null;
34     }

 1 package com.cxh.test1;
 2  
 3 import java.util.HashMap;
 4 import java.util.HashSet;
 5 import java.util.Set;
 6  
 7  
 8 class People{
 9     private String name;
10     private int age;
11      
12     public People(String name,int age) {
13         this.name = name;
14         this.age = age;
15     }  
16      
17     public void setAge(int age){
18         this.age = age;
19     }
20          
21     @Override
22     public boolean equals(Object obj) {
23         // TODO Auto-generated method stub
24         return this.name.equals(((People)obj).name) && this.age== ((People)obj).age;
25     }
26 }
27  
28 public class Main {
29  
30     public static void main(String[] args) {
31          
32         People p1 = new People("Jack", 12);
33         System.out.println(p1.hashCode());
34              
35         HashMap<People, Integer> hashMap = new HashMap<People, Integer>();
36         hashMap.put(p1, 1);
37          
38         System.out.println(hashMap.get(new People("Jack", 12)));
39     }
40 }

1  @Override
2     public int hashCode() {
3         // TODO Auto-generated method stub
4         return name.hashCode()*37+age;
5     }