JAVA Set

Set 存储的值不重复．

package ds.collections.sets;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;

/**
 * set测试　
 * @author Hust
 * @Time 2011-11-9
 */
public class SetTest {
	
	public static void main(String[] args) {
		//testHashSet();
		//testHashSetObj();
		testTreeSet();
		
	}

	//treeSet   
	public static void testTreeSet(){
		Set<String> treeSetTest = Collections.synchronizedSortedSet(new TreeSet<String>());
		treeSetTest.add("123");
		treeSetTest.add("123");
		
		Iterator<String> it =treeSetTest.iterator();
        while(it.hasNext()){
             System.out.println(it.next());
        }//
        //123
        
        TreeSet<String> treeSetTest2 = new TreeSet<String>();
		treeSetTest2.add("def");
        treeSetTest2.add("abc");
		Iterator<String> it2 =treeSetTest2.iterator();
        while(it2.hasNext()){
              System.out.println(it2.next());
        }
		/** result is
		 abc
		 def
		 */
		
        //排序接口
        TreeSet<Po2> treeSetComp = new TreeSet<Po2>(new Compara());
        treeSetComp.add(new Po2(345,"1234565"));
        treeSetComp.add(new Po2(1,"a"));
        treeSetComp.add(new Po2(1,"ab"));
        treeSetComp.add(new Po2(1,"1"));
        treeSetComp.add(new Po2(1,"123"));
        treeSetComp.add(new Po2(1,"41255"));
        treeSetComp.add(new Po2(1,"132"));
        treeSetComp.add(new Po2(1,"一"));
        treeSetComp.add(new Po2(1,"二"));
		Iterator<Po2> itc =treeSetComp.iterator();
        while(itc.hasNext()){
              System.out.println(((Po2)itc.next()).toString());
        }
        /**
         	1,1
			1,a
			1,ab
			1,一
			1,二
			1,123
			1,132
			1,41255
			345,1234565

         */
	}
	
	//HashSet
	public static void testHashSet() {
		//方法不同步： Set set = Collections.synchronizedSet(new HashSet());来实现同步
		Set<String> set = new HashSet<String>();
		System.out.println(set.isEmpty());
		set.add("123");
		set.add(new String("123")); //String 的hashCode使用比的是值*31 ...
		set.add("456");
		set.add("789");
		
		set.add("123"); // 重复的abc,set会自动将其去掉
		//set还是利用equals()方法进行比较
		System.out.println(set.contains("123"));
		System.out.println(set.remove("456"));
		System.out.println(set.contains("456"));
		
		System.out.println("size=" + set.size());
		List<String> list = new ArrayList<String>();
		list.add("zxc");
		list.add("asd");
		list.add("456");
		set.addAll(list); // 将list中的值加入set,并去掉重复的abc
		System.out.println("size=" + set.size());
		for (Iterator<String> it = set.iterator(); it.hasNext();) {
			System.out.println("value=" + it.next().toString());
		}
	}

	//测试存放对象
	public static void testHashSetObj(){
		Set<Po> poSet = Collections.synchronizedSet(new HashSet<Po>());
		Po p1 = new Po(1,"123");
		Po p2 = new Po(1,"123");
		poSet.add(p1);
		poSet.add(p2);
		System.out.println(poSet.size());
		for (Iterator<Po> iterator = poSet.iterator(); iterator.hasNext();) {
			Po po = iterator.next();
			System.out.println(po.toString());
		}
		/**
		 1,123
		 1,123 
		 */
		poSet.clear();
		System.out.println(poSet.size());
		Set<Po2> po2Set = Collections.synchronizedSet(new HashSet<Po2>());
		Po2 p21 = new Po2(1,"123");
		Po2 p22 = new Po2(1,"123");
		po2Set.add(p21);
		po2Set.add(p22);
		for (Iterator<Po2> iterator = po2Set.iterator(); iterator.hasNext();) {
			Po2 po2 = iterator.next();
			System.out.println(po2.hashCode() + po2.toString());
		}
		/**
		 不重写hashCode 与 equals时
		 15580811,123
		 15580811,123
		 重写后
		 15580811,123
		 */
	}

}
/**
 * 测试类
 * @author Hust
 * @Time 2011-11-9
 */
class Po {
	private int id;
	private String name;
	
	public Po(int id,String name){
		this.id = id;
		this.name = name;
	}
	
	public String toString(){
		return id+","+name;
	}
}

/**
 * 测试类
 * @author Hust
 * @Time 2011-11-9
 */
class Po2 {
	private int id;
	private String name;
	
	public Po2(int id,String name){
		this.id = id;
		this.name = name;
	}
	
	//重写hashCode
	public int hashCode() {
		int hash = 0;
		hash += (this.name!=null)?this.name.hashCode():0;
		hash += 31*hash + this.id;
		return hash;
	} 
	
	//重写equals
	public boolean equals(Object o ){
		if(o == null) return false;
		if(o.getClass() != this.getClass()) return false;
		Po2 po = (Po2)o;
		if(this.id != po.id || !this.name.equals(po.name))
			return false;
		return true;
	}
	
	public String toString(){
		return id+","+name;
	}

	public int getId() {
		return id;
	}

	public void setId(int id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

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

class Compara implements Comparator<Po2>{

	@Override
	public int compare(Po2 o1, Po2 o2) {
		if(o1.equals(o2))
			return 0;
		else if(o1.getId() >o2.getId()) 
			return 1;
		else if(o1.getName().hashCode() > o2.getName().hashCode())
			return 1;
		return -1;
	}

}

 

 

评论

1 楼 yys2020 2012-05-17  

受教了