Java之Comparable，Comparator

package comparator;

import java.util.Arrays;

public class User implements Comparable<User> {
	private String id;
	private int age;

	public User(String id, int age) {
		this.id = id;
		this.age = age;
	}

	public int getAge() {
		return age;
	}

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

	public String getId() {
		return id;
	}

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

	@Override
	public int compareTo(User u) {
		return this.age - u.getAge();
	}

	public static void main(String[] args) {
		
		User[] users = new User[] { new User("a", 30), new User("b", 20) };
		//源碼中可以看到調用了compareTo方法進行比較
		Arrays.sort(users);//從小到達排列
		
		//輸出   b 20    a 30
		for (int i = 0; i < users.length; i++) {
			User user = users[i];
			System.out.println(user.getId() + " " + user.getAge());
		}
	}
}









package comparator;

import java.util.Arrays;
import java.util.Comparator;

//強行對某個對象collection進行整體排序的比較函數，
//可以將Comparator傳遞給Collections.sort或Arrays.sort。
public class ComparatorDemo implements Comparator<String> {

	// 如果繼承的是Comparator，則compare的兩個方法是Object類型的
	@Override
	public int compare(String o1, String o2) {
		// 比較String的大小即可
		return toInt(o1) - toInt(o2);
	}

	private int toInt(String str) {
		//String str = (String) str;
		str = str.replaceAll("一", "1");
		str = str.replaceAll("二", "2");
		str = str.replaceAll("三", "3");
		return Integer.parseInt(str);
	}

	public static void main(String[] args) {
		String[] array = new String[] { "一二", "三", "二" };
		// 查看其源碼，可以看到其是通過調用ComparatorDemo的compare方法比較大小的
		// 兩個參數則爲array裏面的值
		Arrays.sort(array, new ComparatorDemo());  //有小到達排列
		//最後輸出     二      三     一二
		for (int i = 0; i < array.length; i++) {
			System.out.println(array[i]);
		}
		//可以嘗試下面的方法
		//Collections.sort(list, c);
		
	}

}









package comparator;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class UserComparator implements Comparator<User> {

	@Override
	public int compare(User o1, User o2) {
		return o1.getAge() - o2.getAge();//默認升序排列
	}

	public static void main(String[] args) {
		User[] users = new User[] { new User("a", 30), new User("b", 20) };
		//運用UserComparator的compare方法進行比較
		Arrays.sort(users, new UserComparator());
		//輸出  b 20	a 30
		for (int i = 0; i < users.length; i++) {
			User user = users[i];
			System.out.println(user.getId() + " " + user.getAge());
		}
		
		
		
		List<User> list = new ArrayList<User>();
		list.add(new User("a", 30));
		list.add(new User("b", 20));
		//內部轉化成數組進行比較 
		Collections.sort(list);//運用User實現的compareTo方法進行比較
		//輸出  b 20	a 30
		for (int i = 0; i < list.size(); i++) {
			User user = list.get(i);
			System.out.println(user.getId() + " " + user.getAge());
		}
		
		
		
		List<User> list2 = new ArrayList<User>();
		list2.add(new User("a", 30));
		list2.add(new User("b", 20));
		Collections.sort(list2, new UserComparator());
		//輸出  b 20	a 30
		for (int i = 0; i < list2.size(); i++) {
			User user = list2.get(i);
			System.out.println(user.getId() + " " + user.getAge());
		}
	}
	
	
}