java List对象排序
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));