lambda常用方法汇总

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 +
            '}';
}