Java 流匹配

Java流 – Java流匹配

Streams API支持对流元素执行不同类型的匹配操作。

Stream接口中的以下方法用于执行匹配操作:

boolean allMatch(Predicate<? super T> predicate)
boolean anyMatch(Predicate<? super T> predicate)
boolean noneMatch(Predicate<? super  T> predicate)

诸如IntStream，LongStream和DoubleStream的原始类型流也包含与谓词一起使用的相同方法和用于原语类型的可选方法。

所有匹配操作都是终端操作。它们也是短路操作。短路操作可以不必处理整个流以返回结果。

以下代码显示如何对流执行匹配操作。

import java.time.LocalDate;
import java.time.Month;
import java.util.Arrays;
import java.util.List;

public class Main {
  public static void main(String[] args) {
    List<Employee> persons = Employee.persons();

    // Check if all persons are males
    boolean allMales = persons.stream().allMatch(Employee::isMale);
    System.out.println("All  males: " + allMales);

    // Check if any person was born in 1971
    boolean anyoneBornIn1971 = persons.stream().anyMatch(p -> p.getDob().getYear() == 1971);
    System.out.println("Anyone born  in 1971:  " + anyoneBornIn1971);

  }
}

class Employee {
  public static enum Gender {
    MALE, FEMALE
  }

  private long id;
  private String name;
  private Gender gender;
  private LocalDate dob;
  private double income;

  public Employee(long id, String name, Gender gender, LocalDate dob,
      double income) {
    this.id = id;
    this.name = name;
    this.gender = gender;
    this.dob = dob;
    this.income = income;
  }
  public boolean isMale() {
    return this.gender == Gender.MALE;
  }

  public LocalDate getDob() {
    return dob;
  }
  public static List<Employee> persons() {
    Employee p1 = new Employee(1, "Jake", Gender.MALE, LocalDate.of(1971,
        Month.JANUARY, 1), 2343.0);
    Employee p2 = new Employee(2, "Jack", Gender.MALE, LocalDate.of(1972,
        Month.JULY, 21), 7100.0);
    Employee p3 = new Employee(3, "Jane", Gender.FEMALE, LocalDate.of(1973,
        Month.MAY, 29), 5455.0);
    Employee p4 = new Employee(4, "Jode", Gender.MALE, LocalDate.of(1974,
        Month.OCTOBER, 16), 1800.0);
    Employee p5 = new Employee(5, "Jeny", Gender.FEMALE, LocalDate.of(1975,
        Month.DECEMBER, 13), 1234.0);
    Employee p6 = new Employee(6, "Jason", Gender.MALE, LocalDate.of(1976,
        Month.JUNE, 9), 3211.0);

    List<Employee> persons = Arrays.asList(p1, p2, p3, p4, p5, p6);

    return persons;
  }

  @Override
  public String toString() {
    String str = String.format("(%s, %s,  %s,  %s,  %.2f)\n", id, name, gender,
        dob, income);
    return str;
  }
}

上面的代码生成以下结果。