Java 集合排序总结

有时候需要对列表数据进行排序，这里总结一下常用方法。

Java API提供了两种方法来排序：

java.util.Collections.sort(java.util.List)

java.util.Collections.sort(java.util.List, java.util.Comparator)

一、Collections.sort（List list）

使用此API排序，要求javabean实现Comparable接口

Dog类：

public class Dog implements Comparable<Dog> {
	private String name;
	private int age;

	public Dog(String name, int age) {
		this.name = name;
		this.age = age;
	}

	public String getName() {
		return name;
	}

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

	public int getAge() {
		return age;
	}

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

	/**
	 * 如果比较的是字符串，则使用String.CompareTo(String s)方法
	 */

	// @Override
	// public int compareTo(Dog dog) {
	// return this.getName().compareTo(dog.getName());
	// }

	/**
	 * 比较int型和char型
	 */
	@Override
	public int compareTo(Dog dog) {
		return this.age - dog.age;
	}
}

测试类：

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

public class Test {

	public static void main(String[] args) {

		List<Dog> mDogs = new ArrayList<>();
		Dog dog1 = new Dog("eog4", 4);
		Dog dog2 = new Dog("dog5", 5);
		Dog dog3 = new Dog("bog2", 2);
		Dog dog4 = new Dog("cog3", 3);
		Dog dog5 = new Dog("aog1", 1);

		mDogs.add(dog1);
		mDogs.add(dog2);
		mDogs.add(dog3);
		mDogs.add(dog4);
		mDogs.add(dog5);

		System.out.println("排序之前：");
		for (Dog dog : mDogs) {
			System.out.println(dog.getName());
		}

		// 排序
		Collections.sort(mDogs);

		System.out.println("排序之后：");
		for (Dog dog : mDogs) {
			System.out.println(dog.getName());
		}

	}
}

测试结果：

排序之前：
eog4
dog5
bog2
cog3
aog1
排序之后：
aog1
bog2
cog3
eog4
dog5

#二、Collections.sort（List list，Comparator comparator）
使用此API实现排序，需要实例化Comparator对象，重写compare(Object o1,Object o2）方法

Dog类：

public class Dog  {
	private String name;
	private int age;

	public Dog(String name, int age) {
		this.name = name;
		this.age = age;
	}

	public String getName() {
		return name;
	}

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

	public int getAge() {
		return age;
	}

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

}

Test测试类：

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

public class Test {

	public static void main(String[] args) {

		List<Dog> mDogs = new ArrayList<>();
		Dog dog1 = new Dog("eog4", 4);
		Dog dog2 = new Dog("dog5", 5);
		Dog dog3 = new Dog("bog2", 2);
		Dog dog4 = new Dog("cog3", 3);
		Dog dog5 = new Dog("aog1", 1);

		mDogs.add(dog1);
		mDogs.add(dog2);
		mDogs.add(dog3);
		mDogs.add(dog4);
		mDogs.add(dog5);

		Comparator<Dog> comparator = new Comparator<Dog>() {
			@Override
			public int compare(Dog o1, Dog o2) {
				return o2.getAge() - o1.getAge();
			}
		};

		System.out.println("排序之前：");
		for (Dog dog : mDogs) {
			System.out.println(dog.getName());
		}

		// 排序
		Collections.sort(mDogs,comparator);

		System.out.println("排序之后：");
		for (Dog dog : mDogs) {
			System.out.println(dog.getName());
		}

	}
}

测试结果：

排序之前：
eog4
dog5
bog2
cog3
aog1
排序之后：
dog5
eog4
cog3
bog2
aog1

如果对String属性排序，使用String.CompareTo(String s)方法进行排序

@Override
	public int compareTo(Dog o) {
		return this.name.compareTo(o.getName());
	}

三、对数组进行排序

如果数组或集合元素是String类型，则可以利用Java API实现的Comparator对象String.CASE_INSENSITIVE_ORDER为容器元素排序。

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

public class Test {

	public static void main(String[] args) {

		String[] array=new String[]{"c","b","d","a","e"};
		List<String> list=Arrays.asList(array);
		
		System.out.println("排序之前：");
		for (String string : list) {
			System.out.println(string);
		}
		
		Collections.sort(list,String.CASE_INSENSITIVE_ORDER);
		
		System.out.println("排序之后：");
		for (String string : list) {
			System.out.println(string);
		}
		
		Collections.sort(list,Collections.reverseOrder());
		System.out.println("反序：");
		for (String string : list) {
			System.out.println(string);
		}
		
	}
}

测试结果：

排序之前：
c
b
d
a
e
排序之后：
a
b
c
d
e
反序：
e
d
c
b
a