Java 流匹配

Java流 - Java流匹配

Streams API支持對流元素執(zhí)行不同類型的匹配操作。

Stream接口中的以下方法用于執(zhí)行匹配操作:

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

諸如IntStream，LongStream和DoubleStream的原始類型流也包含與謂詞一起使用的相同方法和用于原語類型的可選方法。

所有匹配操作都是終端操作。它們也是短路操作。短路操作可以不必處理整個流以返回結(jié)果。

以下代碼顯示如何對流執(zhí)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;
  }
}

上面的代碼生成以下結(jié)果。