如何在Java的lambda表达式中使用Predicate 和BiPredicate ？
在java.util中定义的谓词<T>接口。功能包。它表示一个只有一个参数的布尔值函数。它是一种函数接口，其函数方法是test()。BiPredicate<T,U>接口与具有两个参数的Predicate<T>接口类似。它可以用作lambda表达式的赋值目标。
谓词的语法
@FunctionalInterface public interface Predicate<T>
示例
import java.util.*;
import java.util.function.*;
import java.util.stream.*;
public class EmployeePredicateTest {
public static void main(String[] args) {
Employee e1 = new Employee(1, 23, "M", "Raja");
Employee e2 = new Employee(2, 13, "M", "Jai");
Employee e3 = new Employee(3, 36, "F", "Yamini");
Employee e4 = new Employee(4, 26, "F", "Geetha");
Employee e5 = new Employee(5, 19, "M", "Adithya");
List<Employee> employees = new ArrayList<Employee>();
employees.addAll(Arrays.asList(new Employee[]{e1, e2, e3, e4, e5}));
System.out.println(EmployeePredicate.filterEmployees(employees, EmployeePredicate.isAdultMale()));
System.out.println(EmployeePredicate.filterEmployees(employees, EmployeePredicate.isAdultFemale()));
System.out.println(EmployeePredicate.filterEmployees(employees, EmployeePredicate.isAgeMoreThan(35)));
System.out.println(EmployeePredicate.filterEmployees(employees, EmployeePredicate.isAgeMoreThan(35).negate()));
}
}// Employee classclass Employee {
private Integer id;
private Integer age;
private String gender;
private String name;
public Employee(Integer id, Integer age, String gender, String name) {
this.id = id;
this.age = age;
this.gender = gender;
this.name = name;
}
public Integer getAge() {
return age;
}
public String getGender() {
return gender;
}
public String getName() {
return name;
}
@Override public String toString() {
return this.name.toString()+" - "+ this.age.toString();
}
}// EmployeePredicate classclass EmployeePredicate {
public static Predicate isAdultMale() {
return p -> p.getAge() > 21 && p.getGender().equalsIgnoreCase("M");
}
public static Predicate isAdultFemale() {
return p -> p.getAge() > 18 && p.getGender().equalsIgnoreCase("F");
}
public static Predicate isAgeMoreThan(Integer age) {
return p -> p.getAge() > age;
}
public static List filterEmployees(List<Employee> employees, Predicate<Employee> predicate) {
return employees.stream().filter(predicate).collect(Collectors.<Employee>toList());
}
}输出结果
[Raja - 23] [Yamini - 36, Geetha - 26] [Yamini - 36] [Raja - 23, Jai - 13, Geetha - 26, Adithya - 19]
BiPredicate的语法
@FunctionalInterface public interface BiPredicate<T, U>
示例
import java.util.*;
import java.util.function.*;
public class BiPredicateTest {
public static void main(String[] args) {
BiPredicate<Integer, Integer> bi = (x, y) -> x > y;
BiPredicate<Integer, Integer> eq = (x, y) -> x -2 > y;
System.out.println(bi.test(2, 3));
System.out.println(bi.or(eq).test(2, 3));
System.out.println(bi.or(eq).test(8, 3));
}
}输出结果
false false true