黑马程序员 TreeSet排序的两种实现方式

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本文介绍如何在Java中使用TreeSet类来创建一个具有比较功能的有序集合，并通过实现Comparable接口来定制排序行为。同时展示了如何通过自定义比较器方法进一步灵活地控制集合元素的排序。并通过实例演示了学生信息的排序与打印。

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代码如下

import java.util.TreeSet;

import java.util.Iterator;

class TreeSetDemo {

public static void main(String[] args)

{

Student a = new Student("lisi01",20);

Student b = new Student("lisi001",20);

Student c = new Student("lisi02",18);

Student d = new Student("lisi04",17);

Student e = new Student("lisi03",15);

TreeSet ts = new TreeSet();

ts.add(a);

ts.add(b);

ts.add(c);

ts.add(d);

ts.add(e);

Iterator it = ts.iterator();

while(it.hasNext())

{

Student xxx=(Student)it.next();

System.out.println(xxx.name+","+xxx.age);

}

class Student implements Comparable

{

public int compareTo(Object obj)

{

if(!(obj instanceof Student))

throw new RuntimeException("不是学生类");

Student ss = (Student)obj;System.out.println(this.name+",compareTo,"+ss.name);

if(ss.age>this.age)

return -1;

if(ss.age==this.age)

return this.name.compareTo(ss.name);//使用String自身的比较方法

return 1;

}

Student(String name,int age)

{

this.name=name;

this.age=age;

}

int age;

String name;

}

1.让元素自身具备比较性：

让比较对象的类实现Comparable接口，复写compareTo()方法

2.比较器方法，将比较器的对象作为参数传给构造函数：例如

TreeSet ts = new TreeSet( new MyComparator);

新定义一个类，实现Comparator接口，复写compare()方法。

当两种排序都存在时，以比较器为主。

第二种方法具体实现如下：

package note.heima;

import java.util.Comparator;

import java.util.TreeSet;

import java.util.Iterator;

class TreeSetDemo2 {

public static void main(String[] args)

{

Student2 a = new Student2("lisi01",20);

Student2 b = new Student2("lisi001",20);

Student2 c = new Student2("lisi02",18);

Student2 d = new Student2("lisi04",17);

Student2 e = new Student2("lisi03",15);

Student2 f = new Student2("lisi03",15);

TreeSet ts = new TreeSet(new MyComp());

ts.add(a);

ts.add(b);

ts.add(c);

ts.add(d);

ts.add(e);

ts.add(f);

Iterator it = ts.iterator();

while(it.hasNext())

{

Student2 xxx=(Student2)it.next();

System.out.println(xxx.name+","+xxx.age);

}

class MyComp implements Comparator

{

public int compare(Object o1,Object o2)

{

Student2 s1 = (Student2)o1;

Student2 s2 = (Student2)o2;

int num = s1.name.compareTo(s2.name);

if (num>0)

return 1;

if (num<0)

return -1;

if (num == 0)

{

return new Integer(s1.age).compareTo(new Integer(s2.age));

}

return num;

}

class Student2 implements Comparable

{

public int compareTo(Object obj)

{

if(!(obj instanceof Student2))

throw new RuntimeException("不是学生类");

Student2 ss = (Student2)obj;System.out.println(this.name+",compareTo,"+ss.name);

if(ss.age>this.age)

return -1;

if(ss.age==this.age)

return this.name.compareTo(ss.name);//使用String自身的比较方法

return 1;

}

Student2(String name,int age)

{

this.name=name;

this.age=age;

}

int age;

String name;

}