Home Home » Java » Java Core » [Java] - Predicate Interface

[Java] - Predicate Interface

Friday, April 27, 2018


Predicate Interface is a functional interface that represents a predicate of one argument and it is defined in java.util.function packages. That helps your code is simple.

Ref:
- https://docs.oracle.com/javase/8/docs/api/java/util/function/class-use/Predicate.html
- http://www.java2s.com/Tutorials/Java/java.util.function/Predicate/index.htm

1. Predicate example 1 

Predicate<Integer> pr = b -> (b >= 18); // Creating predicate  
System.out.println(pr.test(18));    // Calling Predicate method 

 Results:
true

2. Predicate example 2 (Lambda and Method Reference)

Student.java
package com.javacore.stream;

public class Student {
 private String name;
 private int age;

 public Student(String name, int age) {
  super();
  this.name = name;
  this.age = age;
 }

 public String getName() {
  return name;
 }

 public void setName(String name) {
  this.name = name;
 }

 public int getAge() {
  return age;
 }

 public void setAge(int age) {
  this.age = age;
 }

 @Override
 public String toString() {
  // TODO Auto-generated method stub
  return "name = " + this.name + ";age= " + this.age;
 }

}

Main.java
package com.javacore.stream;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;

public class Main {

 public static void main(String[] args) {
   // create some student
  Student andy = new Student("andy", 25);
  Student susi = new Student("susi", 26);
  Student tom = new Student("tom", 24);
  Student adam = new Student("adam", 25);

  // create student list
  List<Student> studentList = Arrays.asList(andy, susi, tom, adam);
 
  //use Method Reference
  List<Student> studentOf25Age = filter(studentList, Main::isStudentAgeLessThan);
  System.out.println(studentOf25Age);
  
  //use lambda
  List<Student> studentOf26Age = filter(studentList, (Student student)  -> 26 == student.getAge());
  System.out.println(studentOf26Age);
 }

 public static boolean isStudentAgeLessThan(Student argStudent) {
  if (argStudent.getAge() < 25) {
   return true;
  }

  return false;
 }

 public static List<Student> filter(List<Student> argStudentList,
   Predicate<Student> argPredicate) {
  List<Student> studentList = new ArrayList<>();

  for (Student student : argStudentList) {
   if (argPredicate.test(student)) {
    studentList.add(student);
   }
  }

  return studentList;
 }

}

 Results:
[name = tom;age= 24]
[name = susi;age= 26]

updating...



Chia sẻ bài viết
Bài liên quan

Comments[ 0 ]


Post a Comment