java List對象排序

Lambda用到了JDK8自帶的一個函數式接口Comparator<T>。

准備一個Apple類

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();  
}

　

步驟一：

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

　　

步驟二：准備一個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"));

　　

步驟三：順序排序，三種方式

/**
 * 順序排序
 */
// 1、傳遞代碼，函數式編程
inventory.sort(new AppleComparator());
System.out.println(inventory);

// 2、匿名內部類
inventory.sort(new Comparator<Apple>() {
    @Override
    public int compare(Apple o1, Apple o2) {
        return o1.getWeight() - o2.getWeight();
    }
});

// 3、使用Lambda表達式
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()));
//或者等價於
inventory.sort(comparing(Apple::getWeight));

　　

 步驟四：逆序排序

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

　　

步驟五：如果兩個蘋果一樣重，就得再找一個條件來進行排序、

// 2、如果兩個蘋果的重量一樣重，怎么辦？那就再找一個條件進行排序唄
inventory.sort(comparing(Apple::getWeight).reversed().thenComparing(Apple::getColor));