lambda常用方法汇总

落日映苍穹つ 2022-11-27 00:44 191阅读 0赞

public class AdjustTests \{

public static void main(String[] args){
        Person p1 = new Person(1,"张三","男",18,new BigDecimal(100));
        Person p2 = new Person(2,"李四","女",16,new BigDecimal(200));
        Person p3 = new Person(3,"王五","男",18,new BigDecimal(300));
        Person p4 = new Person(4,"赵六","男",18,new BigDecimal(400.5));
        Person p5 = new Person(5,"田七","女",16,new BigDecimal(500));
    
        List<Person> list = Arrays.asList(p1, p2, p3, p4, p5);
    
        System.out.println(list);
        //集合只保留男性
        List<Person> list1 = list.stream().filter(p -> "男".equals(p.getSex())).collect(Collectors.toList());
        System.out.println(list1);
        //集合只保留男性，且对所有男性的账号金额求和
        BigDecimal sumAccount = list.stream().filter(p -> "男".equals(p.getSex())).map(Person::getAccount).reduce(BigDecimal.ZERO, BigDecimal::add);
        System.out.println(sumAccount);
        //根据年龄和性别分组，并求出分组后账户的总金额
        Map<String, Person> accountMap = list.stream().collect(Collectors.toMap(
                p -> String.valueOf(p.getAge()) + "_" + p.getSex()
                , Function.identity()
                , (t1, t2) -> {
                    t2.setAccount(t2.getAccount().subtract(t1.getAccount()));
                    return t2;
                }
        ));
        System.out.println(accountMap);
    
        //根据工资倒叙排序
        List<Person> newList = list.stream().sorted(Comparator.comparing(Person::getAccount).reversed()).collect(Collectors.toList());
        System.out.println(newList);
        //多条件排序
        List<Person> newList1 = list.stream().filter(p -> p.getAccount() != null).sorted(Comparator.comparing(Person::getSex).thenComparing(Person::getAccount)).collect(Collectors.toList());
        System.out.println(newList1);
    
        //求最小值
        BigDecimal account = newList.stream().min(Comparator.comparing(Person::getAccount)).get().getAccount();
        System.out.println(account);
        //判断是否为空
        Optional.ofNullable(p1).map(u -> u.getName()).get();
        //判读是否为空，抛异常
        Person p = null;
        String s = Optional.ofNullable(p).map(u -> u.getName()).orElse("0");
        try {
            Optional.ofNullable(p).map(u -> u.getName()).orElseThrow(() ->  new Exception("132"));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

class Person \{  
private Integer id;  
private String name;  
private String sex;  
private Integer age;  
private BigDecimal account;

private BigDecimal count;
    
    
    public Person(Integer id, String name, String sex, Integer age, BigDecimal account) {
        this.id = id;
        this.name = name;
        this.sex = sex;
        this.age = age;
        this.account = account;
    }
    
    public Integer getId() {
        return id;
    }
    
    public void setId(Integer id) {
        this.id = id;
    }
    
    public Integer getAge() {
        return age;
    }
    
    public void setAge(Integer age) {
        this.age = age;
    }
    
    public String getSex() {
        return sex;
    }
    
    public void setSex(String sex) {
        this.sex = sex;
    }
    
    public BigDecimal getAccount() {
        return account;
    }
    
    public void setAccount(BigDecimal account) {
        this.account = account;
    }
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public BigDecimal getCount() {
        return count;
    }
    
    public void setCount(BigDecimal count) {
        this.count = count;
    }
    
    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", age=" + age +
                ", account=" + account +
                '}';
    }