Java容器Treeset的两种排序方法

TreeSet支持两种排序方式：自然排序、定制排序

1、自然排序：自然排序下，集合元素必须是实现了Comparable接口的类的对象。

也就是说，在这种排序方式下需要实现Comparable接口。

覆盖此接口中的compareTo(Object obj)方法，定义目标的比较方法

package edu.hnsd1.dao;

import java.util.Iterator;
import java.util.TreeSet;
/**
* 上机实验：CPU有型号、单价、主频等属性
* 构造这样的对象添加到Treeset中，并对其进行降序输出。
* @author Blue Jey
*自然排序方式
*/

public class TreeSetImpl {

public static void main(String[] args) {
// TODO Auto-generated method stub
TreeSet treeset=new TreeSet();
treeset.add(new computer1("联想ThinkPadE431",3333,3));
treeset.add(new computer1("宏基",3000,3));
treeset.add(new computer1("Dell",4000,3));

Iterator itera=treeset.iterator();
while(itera.hasNext()){
System.out.println(itera.next());
}

}

}
class computer1 implements Comparable {
private String Type;//电脑的型号
private int Price;//电脑的单价
private int MainFrequency;//电脑的主频/MHZ
public computer1(String t1,int t2,int t3){
this.setComputer1(t1, t2, t3);
}
public void setComputer1(String t1,int t2,int t3){
this.Type=t1;
this.Price=t2;
this.MainFrequency=t3;
}

@Override
public int compareTo(Object arg0) {
// TODO Auto-generated method stub
int ret=0;
if(!(arg0 instanceof computer1))
throw new RuntimeException("对象不对！");
computer1 temp=(computer1)arg0;
if(this.equals(temp)){
System.out.println("HELLO WORD!");
}
ret=this.Price-temp.Price;
if(ret==0){
ret=this.MainFrequency-temp.MainFrequency;
}
return -ret;
}
public String toString(){
return this.Type+" "+this.Price+" "+this.MainFrequency;
}</span>

2、定制排序：通过构造方法指定TreeSet的比较器进行排序，实现 int compare(T o1,T o2)的比较方法。

package edu.hnsd1.dao;

import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;

/**
* 上机实验：CPU有型号、单价、主频等属性 构造这样的对象添加到Treeset中，并对其进行降序输出。
*
* @author Blue Jey 自然排序方式
*/

public class TreeSetImpl {

public static void main(String[] args) {
// TODO Auto-generated method stub
TreeSet treeset = new TreeSet(new newComparator());
treeset.add(new computer2("联想ThinkPadE431", 3333, 3));
treeset.add(new computer2("宏基", 3000, 3));
treeset.add(new computer2("Dell", 4000, 3));

Iterator itera = treeset.iterator();
while (itera.hasNext()) {
System.out.println(itera.next());
}

}

}

class computer2 {
private String Type;// 电脑的型号
private int Price;// 电脑的单价
private int MainFrequency;// 电脑的主频/MHZ

public computer2(String t1, int t2, int t3) {
this.setcomputer2(t1, t2, t3);
}

public void setcomputer2(String t1, int t2, int t3) {
this.Type = t1;
this.Price = t2;
this.MainFrequency = t3;
}

public int getPrice() {
return this.Price;
}

public int getMF() {
return this.MainFrequency;
}

public String toString() {
return this.Type + " " + this.Price + " " + this.MainFrequency;
}

}

class newComparator implements Comparator {

@Override
public int compare(Object arg0, Object arg1) {
int ret = 0;
computer2 temp = (computer2) arg0;
computer2 temp1 = (computer2) arg1;
ret = temp.getPrice() - temp1.getPrice();
if (ret == 0) {
ret = temp.getMF() - temp1.getMF();
}
return -ret;
}

}