Java8 的骚操作二（增强版Comparator和排序）

前言

Lambda表达式中Comparator和对集合（Collection）进行排序

数据结构准备

public class Item {
    private Long id;
    private String name;
    private Double score;
    private BigDecimal bigDecimal;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public Double getScore() {
        return score;
    }

    public void setScore(Double score) {
        this.score = score;
    }

    public BigDecimal getBigDecimal() {
        return bigDecimal;
    }

    public void setBigDecimal(BigDecimal bigDecimal) {
        this.bigDecimal = bigDecimal;
    }
}

    /**
     * init List
     * @return
     */
    private List<Item> initList(){
        List<Item> itemList = new ArrayList<>();
        for (int i=0;i<10;i++){
            Item item = new Item();
            item.setId((long) i);
            item.setName("Test"+i);
            item.setScore(Math.random());
            item.setBigDecimal(new BigDecimal(Math.random()));
            itemList.add(item);
        }
        return itemList;
    }

不使用Lambda表达式的基本排序

    public void noLambdaSort(){
        List<Item> itemList = initList();
        Collections.shuffle(itemList);
        Collections.sort(itemList, new Comparator<Item>() {
            @Override
            public int compare(Item o1, Item o2) {
                return o1.getName().compareTo(o2.getName());
            }
        });
    }

使用Lambda表达式的排序

    public void lambdaSort(){
        List<Item> itemList = initList();
        Collections.shuffle(itemList);
        itemList.sort((Item item1,Item item2)->item1.getName().compareTo(item2.getName()));
        itemList.sort(( item1, item2)->item1.getName().compareTo(item2.getName()));
        itemList.sort(Comparator.comparing(Item::getName));
        Collections.sort(itemList, Comparator.comparing(Item::getName));
        Collections.sort(itemList, (o1, o2) -> o1.getName().compareTo(o2.getName()));
    }

反转排序

 public void lambdaReversedSort(){
        List<Item> itemList = initList();
        Collections.shuffle(itemList);
        Comparator<Item> comparator = Comparator.comparing(Item::getName);
        itemList.sort(comparator.reversed());
    }

多条件组合排序

    public void multipleConditionsSort(){
        List<Item> itemList = initList();
        Collections.shuffle(itemList);
        itemList.sort(Comparator.comparing(Item::getName).thenComparingDouble(Item::getScore));
    }