一个非常高效的去重且保持原顺序算法

package hashmap;

public class User {

	private String name;

	private String pwd;

	public String getName() {
		return name;
	}

	public User(String name, String pwd) {
		this.name = name;
		this.pwd = pwd;

	}

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

	public String getPwd() {
		return pwd;
	}

	public void setPwd(String pwd) {
		this.pwd = pwd;
	}

	@Override
	public boolean equals(Object obj) {
		return this.name.equals(((User)obj).getName()) && this.pwd.equals(((User)obj).getPwd());
	}

	@Override
	public String toString() {
		return name + " " + pwd;
	}

	@Override
	public int hashCode() {
		return toString().hashCode();
	}

}

　　对象类中必须覆盖equals和hashcode方法

package hashmap;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Test {

	public static void main(String[] args) {
		List<User> users=new ArrayList<User>();
		users.add(new User("zcs","zcs"));
		users.add(new User("zcs","zcs"));
		users.add(new User("zcs","zcs1"));
		users.add(new User("zcs","zcs1"));
		users.add(new User("zcs","zcs2"));
		users.add(new User("zcs","zcs3"));
		
		final Map<User, Integer> map=new HashMap<User, Integer>();
		//将对象作为key存入hashmap中，通过key的唯一性可以去掉重复的对象
		//value值中存当前对象所对应的位置，作为排序时的标准
		for(int i=0;i<users.size();i++) {
			map.put(users.get(i), i);
		}
		User[] newUsers = map.keySet().toArray(new User[0]);
		Arrays.sort(newUsers, new Comparator<User>() {

			@Override
			public int compare(User o1, User o2) {
				//获取key对应的value，进行比较排序，这样就能保证原来的顺序不变
				int i1=map.get(o1);
				int i2=map.get(o2);
				return i1-i2;
			}
		});
		
		List<User> list = Arrays.asList(newUsers);
		for(User u:list) {
			System.err.println(u.getName()+" "+u.getPwd());
		}
		
	}

}