HashSet遍历

[JavaPeak]

HashSet不是乱序吗？为什么加入Integer时，遍历时是升序？

[果子狸G]

运气吧 看代码

[龙四]

hashCode的缘故

[果子狸G]

http://topic.csdn.net/u/20120806/10/0150612b-1a88-4574-b2b6-3a8fd29ab179.html

[scbb]

hashcode正好和Integer的数字顺序一致。

[zhaoming262350]

package com.test;

import java.util.HashSet;
import java.util.Set;

public class SetTest
{
public static void main(String [] args)
{
Set <Integer> set = new HashSet<Integer>();
set.add(100);
set.add(156);
set.add(198);
set.add(359);
set.add(12);
set.add(200);
set.add(23);
System.out.println(set);
}
}
输出：

[100, 359, 156, 200, 23, 198, 12]

[zhaoming262350]

建议你看一下HasnSet的源代码

public class HashSet<E>
extends AbstractSet<E>
implements Set<E>, Cloneable, java.io.Serializable
{
static final long serialVersionUID = -5024744406713321676L;

private transient HashMap<E,Object> map;

// Dummy value to associate with an Object in the backing Map
private static final Object PRESENT = new Object();

/**
* Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
* default initial capacity (16) and load factor (0.75).
*/
public HashSet() {
map = new HashMap<E,Object>();
}

/**
* Constructs a new set containing the elements in the specified
* collection. The <tt>HashMap</tt> is created with default load factor
* (0.75) and an initial capacity sufficient to contain the elements in
* the specified collection.
*
* @param c the collection whose elements are to be placed into this set
* @throws NullPointerException if the specified collection is null
*/
public HashSet(Collection<? extends E> c) {
map = new HashMap<E,Object>(Math.max((int) (c.size()/.75f) + 1, 16));
addAll(c);
}

/**
* Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
* the specified initial capacity and the specified load factor.
*
* @param initialCapacity the initial capacity of the hash map
* @param loadFactor the load factor of the hash map
* @throws IllegalArgumentException if the initial capacity is less
* than zero, or if the load factor is nonpositive
*/
public HashSet(int initialCapacity, float loadFactor) {
map = new HashMap<E,Object>(initialCapacity, loadFactor);
}

/**
* Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
* the specified initial capacity and default load factor (0.75).
*
* @param initialCapacity the initial capacity of the hash table
* @throws IllegalArgumentException if the initial capacity is less
* than zero
*/
public HashSet(int initialCapacity) {
map = new HashMap<E,Object>(initialCapacity);
}

/**
* Constructs a new, empty linked hash set. (This package private
* constructor is only used by LinkedHashSet.) The backing
* HashMap instance is a LinkedHashMap with the specified initial
* capacity and the specified load factor.
*
* @param initialCapacity the initial capacity of the hash map
* @param loadFactor the load factor of the hash map
* @param dummy ignored (distinguishes this
* constructor from other int, float constructor.)
* @throws IllegalArgumentException if the initial capacity is less
* than zero, or if the load factor is nonpositive
*/
HashSet(int initialCapacity, float loadFactor, boolean dummy) {
map = new LinkedHashMap<E,Object>(initialCapacity, loadFactor);
}