JAVA重寫hashCode通用辦法(摘錄自《Effective Java》)

1. 初始化一個整形變量，為此變量賦予一個非零的常數值，比方int result = 17;
2. 選取equals辦法中用於比擬的一切域，然後針對每個域的屬性停止計算：
(1) 假如是boolean值，則計算f ? 1:0
(2) 假如是byte\char\short\int,則計算(int)f
(3) 假如是long值，則計算(int)(f ^ (f >>> 32))
(4) 假如是float值，則計算Float.floatToIntBits(f)
(5) 假如是double值，則計算Double.doubleToLongBits(f)，然後前往的後果是long,再用規則(3)去處置long,失掉int
(6) 假如是對象使用，假如equals辦法中采取遞歸調用的比擬方式，那麼hashCode中異樣采取遞歸調用hashCode的方式。　　否則需求為這個域計算一個范式，比方當這個域的值為null的時分，那麼hashCode 值為0
(7) 假如是數組，那麼需求為每個元素當做獨自的域來處置。假如你運用的是1.5及以上版本的JDK，那麼沒必要自己去　　　　重新遍歷一遍數組，java.util.Arrays.hashCode辦法包括了8種根本類型數組和援用數組的hashCode計算，算法同上，
　　java.util.Arrays.hashCode(long[])的詳細完成:

public static int hashCode(long a[]) {  
        if (a == null)  
            return 0;  
  
        int result = 1;  
        for (long element : a) {  
            int elementHash = (int)(element ^ (element >>> 32));  
            result = 31 * result + elementHash;  
        }  
  
        return result;  
}

example: 

package com.kingdee.cloudhub.stat.domains;

import java.util.Arrays;

public class Person {
	private int age;
	
	private String name;
	
	private char sex;
	
	private String[] hoby;

	public Person(int age, char sex, String name, String[] hoby) {
		this.age = age;
		this.sex = sex;
		this.name = name;
		this.hoby = hoby;
	}
	
	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public char getSex() {
		return sex;
	}

	public void setSex(char sex) {
		this.sex = sex;
	}

	public String[] getHoby() {
		return hoby;
	}

	public void setHoby(String[] hoby) {
		this.hoby = hoby;
	}

	public int hashCode() {
		int result = 1;
		result = 31 * result + age;
		result = 31 * result + sex;
		result = 31 * result + name.hashCode();
		for(String s : hoby) {
			result = 31 * result + s.hashCode();
		}
		return result;
	}

	public boolean equals(Object obj) {
		if(null == obj)
			return false;
		if(this == obj)
			return true;
		if (!(obj instanceof Person))
	           return false;
		Person p = (Person)obj;
		return this.age == p.age && this.sex == p.sex
				&& this.name.equals(p.name) && Arrays.equals(this.hoby, p.hoby);
	}

}