Simple example of Lambda expression and Stream class in Java-javaTutorial-php.cn

Simple example of Lambda expression and Stream class in Java

黄舟

Release： 2017-01-17 15:14:07

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How to use Java's lambda expressions and Stream? ? ?

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The syntax of Lambda expression

Basic syntax:

[code](parameters) -> expression
或
(parameters) ->{ statements; }

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Look at the examples to learn!

Example 1: Define an AyPerson class to prepare for subsequent testing.

[code]package com.evada.de;

import java.util.Arrays;
import java.util.List;

class AyPerson{

    private String id;
    private String name;

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

    public AyPerson(String id, String name) {
        this.id = id;
        this.name = name;
    }
}

/**
 * Created by Ay on 2016/5/9.
 */
public class LambdaTest {

    public static void main(String[] args) {
        List<String> names = Arrays.asList("Ay", "Al", "Xy", "Xl");
        names.forEach((name) -> System.out.println(name + ";"));
    }
}

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The above example names.forEach((name) -> System.out.println(name + “;”));

is similar to:

function(name){//name为参数 

System.out.println(name + “;”);//方法体 

}

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Result:

[code]Ay;
Al;
Xy;
Xl;

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Example 2: Copy the following code into the main function above

[code]List<Student> personList = new ArrayList<>();
personList.add(new Student("00001","Ay"));
personList.add(new Student("00002","Al"));
personList.add(new Student("00003","To"));
personList.forEach((person) -> System.out.println(person.getId()+ ":" + person.getName()));

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Result:

[code]00001:Ay
00002:Al
00003:To

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Example 3: f**ilter( in Lambda and Stream classes )**Method

[code]List<AyPerson> personList = new ArrayList<>();
    personList.add(new AyPerson("00001","Ay"));
    personList.add(new AyPerson("00002","Al"));
    personList.add(new AyPerson("00003", "To"));
    //stream类中的filter方法
    personList.stream()
            //过滤集合中person的id为00001
            .filter((person) -> person.getId().equals("00001"))
            //将过滤后的结果循环打印出来
            .forEach((person) -> System.out.println(person.getId() + ":" + person.getName()));

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Result:

[code]00001:Ay

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Example 4: collect() method in Stream class,

[code]    List<AyPerson> personList = new ArrayList<>();
    List<AyPerson> newPersonList = null;

    personList.add(new AyPerson("00001","Ay"));
    personList.add(new AyPerson("00002","Al"));
    personList.add(new AyPerson("00003", "To"));
    //将过滤后的结果返回到一个新的List中
    newPersonList = personList.stream()
            .filter((person) -> person.getId().equals("00002")).collect(Collectors.toList());
    //打印结果集
    newPersonList.forEach((person) -> System.out.println(person.getId() + ":" + person.getName()));

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##In addition to Put it in List, you can also put it in Set, etc...
Result:

[code]00002:Al

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There are many useful methods that can be used in Stream, such as count, limit, etc. Go to the API to learn by yourself

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