java中comparator与comparable的解析

java中comparator与comparable的解析
一.comparable与comparator的不同点
1.首先comparable是在java.lang包下的接口，而comparator是java.util包下的接口。
2.类实现comparable接口后需要实现下面的方法：

public int compareTo(T o) {
		return 0  ;
	}

而实现Comparator的类，测需要实现下面的方法：

public int compare(Object o1, Objecto2) {
		return 0；
		}

3.实现comparable的接口的类，它的对象就可以进行自比较，通过Arrays.sort()或Collections.sort()就可以对包含此对象的数组或集合进行排序。看下面例子：
首先，先定义一个Person类，实现Comparable接口，我们以年龄作为排序的依据：

public class Person<T> implements Comparable<T> {

	private String name;
	
	private String sex;	
        
         private int age;
	
	public String getName() {
		return name;
	}

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

	public String getSex() {
		return sex;
	}

	public void setSex(String sex) {
		this.sex = sex;
	}

	public Person(String name, String sex, int age) {
		super();
		this.name = name;
		this.sex = sex;
		this.age = age;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	@Override
	public int compareTo(T o) {
		// TODO Auto-generated method stub
		
		return ((Person)o).getAge() - this.age  ;
	}

}

然后，定义一个测试类，如下：

public class TestCompare {

	public static void main(String[] args){
		List<Person> list = new ArrayList<Person>();
		Person p1 = new Person("a","male",1);
		Person p2 = new Person("b","female",2);
		Person p3 = new Person("c","male",3);
		
		list.add(p3);
		list.add(p1);
		list.add(p2);
		
		Collections.sort(list);
		
		for(Person p:list){
			System.out.println("Name: " + p.getName() + "  "
					+ "Sex: " + p.getSex() + "  " + "Age: " + p.getAge());
		}		
	
}

输出结果为：

Name: c  Sex: male  Age: 3 
Name: b  Sex: female  Age: 2 
Name: a  Sex: male  Age: 1 

这是是降序排列，把compareTo中的方法做如下改动，就变成升序排列了。

	
	public int compareTo(T o) {
		// TODO Auto-generated method stub
		
		return this.age - ((Person)o).getAge() ;
	}

4.有时类并没有实现comparable接口，而我们又需要对包含此类对象的数组或集合进行排序，那么我们就需要实现Comparator这个比较器了。新建一个person类：

public class Person<T> {

	private String name;
	
	private String sex;
	
	private int age;
	
	public String getName() {
		return name;
	}

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

	public String getSex() {
		return sex;
	}

	public void setSex(String sex) {
		this.sex = sex;
	}

	public Person(String name, String sex, int age) {
		super();
		this.name = name;
		this.sex = sex;
		this.age = age;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

}

再定义一个测试类：

public class TestCompare {

	public static void main(String[] args){
		List<Person> list = new ArrayList<Person>();
		Person p1 = new Person("a","male",1);
		Person p2 = new Person("b","female",2);
		Person p3 = new Person("c","male",3);
		
		list.add(p3);
		list.add(p1);
		list.add(p2);
		
		Collections.sort(list , emCpmpare);
		
		for(Person p:list){
			System.out.println("Name: " + p.getName() + "  "
					+ "Sex: " + p.getSex() + "  " + "Age: " + p.getAge());
		}
	}
	
	public static Comparator<Person> emCpmpare = new Comparator<Person>(){

		@Override
		public int compare(Person o1, Person o2) {
			// TODO Auto-generated method stub
			String name1 = ((Person)o1).getName();
			String name2 = ((Person)o2).getName();
			if(!name1.isEmpty() && !name2.isEmpty())
				return name1.compareTo(name2);
			else {
				int age1 = ((Person)o1).getAge();
				int age2 = ((Person)o2).getAge();
				return age1 - age2;
			}
		}
	};
}

转自：http://xhlmy.iteye.com/blog/1553970