Java8 Lambda表达式如何实现List集合的排序功能？

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Lambda表达式利用了JDK8的函数式接口特性，简化了Comparator的创建。以下是对应的简写代码：

javaLambda表达式应用于JDK8自带的一个函数式接口Comparator。准备一个Apple类：public class Apple { private int weight; private String color;

public Apple() {}

public Apple(int weight) { this.weight=weight; }

public Apple(int weight, String color) { this.weight=weight; this.color=color; }

// Getter和Setter省略}

Lambda用到了JDK8自带的一个函数式接口Comparator<T>。

准备一个Apple类

public class Apple { private int weight; private String color; public Apple(){} public Apple(int weight) { this.weight = weight; } public Apple(int weight, String color) { this.weight = weight; this.color = color; } setters();getters();toString(); }

步骤一：

public class AppleComparator implements Comparator<Apple> { @Override public int compare(Apple o1, Apple o2) { return o1.getWeight() - o2.getWeight(); } }

步骤二：准备一个List集合

ArrayList<Apple> inventory = Lists.newArrayList( new Apple(10, "red"), new Apple(5, "red"), new Apple(1, "green"), new Apple(15, "green"), new Apple(2, "red"));

步骤三：顺序排序，三种方式

/** * 顺序排序 */ // 1、传递代码，函数式编程 inventory.sort(new AppleComparator()); System.out.println(inventory); // 2、匿名内部类 inventory.sort(new Comparator<Apple>() { @Override public int compare(Apple o1, Apple o2) { return o1.getWeight() - o2.getWeight(); } }); // 3、使用Lambda表达式 inventory.sort((a, b) -> a.getWeight() - b.getWeight()); // 4、使用Comparator的comparing Comparator<Apple> comparing = comparing((Apple a) -> a.getWeight()); inventory.sort(comparing((Apple a) -> a.getWeight())); //或者等价于 inventory.sort(comparing(Apple::getWeight));

步骤四：逆序排序

/** * 逆序排序 */ // 1、 根据重量逆序排序 inventory.sort(comparing(Apple::getWeight).reversed());

步骤五：如果两个苹果一样重，就得再找一个条件来进行排序

// 2、如果两个苹果的重量一样重，怎么办？那就再找一个条件进行排序呗 inventory.sort(comparing(Apple::getWeight).reversed().thenComparing(Apple::getColor));

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参考：

《Java8实战》

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