Java8------Sort()

前言

Java 8中的排序算法功能极其强大，无论在写法上还是可读性上都完全超越前代sort。总的来说Java 8中的sort()有两种，第一种替代了老版的sort，用lambda语句优化；第二种用在stream中，可以参照我后面的文章。如果你还在创建Comparator去排序，一定要看看我这篇blog。

代码及分析

首先我们来比较一下比较简单的sort。
对于Array的sort：

1. Arrays.sort()只能对基础类型数组进行升序排序!!
2. Arrays.sort()可以对String或User类等进行自定义排序。

---

对于List.sort(), 可以用lambda表达式自定义sort

public static void main(String[] args) {
	ArrayList<Integer> list = new ArrayList<>();
	initIntArray(list);
	list.sort((i1,i2)->i2-i1);
	System.out.println(list);
}
private static void initIntArray(List l) {
		for (int i = 0; i < 10; i++) {
			l.add((int)(100 * Math.random() / 1));
		}
	}

输出结果为：

[83, 68, 61, 53, 33, 29, 28, 21, 15, 11]

---

下面来说一下类的sort
如果类只有单一条件的比较，直接用上文所提到的lambda表达式排序即可。但若有多重的条件，比如先按name排序，name相同的话按age排序。可用Comparator中的thenComparing方法定义次要排序条件。reverse方法可以调整顺序或者倒序。代码如下：

public class Sort {
	
	public static class Overwatch {
		
		String name;

		int age;
		
		public Overwatch(String name, int age) {
			// TODO Auto-generated constructor stub
			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;
		}
		
		@Override
		public String toString() {
			// TODO Auto-generated method stub
			return name+":"+age;
		}
		
		
	}

	public static void main(String[] args) {
		List<Overwatch> l = new ArrayList<>();
		initList(l);
//		l.sort((Overwatch o1, Overwatch o2)->(o1.name.compareTo(o2.name)));
		l.sort(Comparator.comparing(Overwatch::getName).reversed().
						  thenComparingInt(Overwatch::getAge).reversed());
//		l.sort(Comparator.comparing(Overwatch::getName).reversed().
//						  thenComparingInt(Overwatch::getAge));
//		l.sort(Comparator.comparing(Overwatch::getName).
//						  thenComparingInt(Overwatch::getAge));
//		l.sort(Comparator.comparing(Overwatch::getName).
//						  thenComparingInt(Overwatch::getAge).reversed());
		System.out.println(l);
	}

	private static void initList(List<Overwatch> list) {
		// TODO Auto-generated method stub
		list.add(new Overwatch("Tracer",23));
		list.add(new Overwatch("Tracer",19));
		list.add(new Overwatch("Tracer",24));
        list.add(new Overwatch("Genji",39));
        list.add(new Overwatch("Reinhardt",61));
        list.add(new Overwatch("Reinhardt",45));
        list.add(new Overwatch("Mercy",37));
        list.add(new Overwatch("Mercy",27));
        list.add(new Overwatch("Mccree",39));
        list.add(new Overwatch("Ana",49));
        list.add(new Overwatch("Dva",26));
	}
}

四种排序结果分别如下(注意reverse的位置):

name: 小->大; age: 大->小
[Ana:49, Dva:26, Genji:39, Mccree:39, Mercy:37, Mercy:27, Reinhardt:61, Reinhardt:45, Tracer:24, Tracer:23, Tracer:19]

name: 大->小; age: 小->大
[Tracer:19, Tracer:23, Tracer:24, Reinhardt:45, Reinhardt:61, Mercy:27, Mercy:37, Mccree:39, Genji:39, Dva:26, Ana:49]

name: 小->大; age: 小->大
[Ana:49, Dva:26, Genji:39, Mccree:39, Mercy:27, Mercy:37, Reinhardt:45, Reinhardt:61, Tracer:19, Tracer:23, Tracer:24]

name: 大->小; age: 大->小
[Tracer:24, Tracer:23, Tracer:19, Reinhardt:61, Reinhardt:45, Mercy:37, Mercy:27, Mccree:39, Genji:39, Dva:26, Ana:49]