Java Lambda filter foreach的简单使用

Java Lambda filter foreach的简单使用

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Java在对 List 集合进行按条件查询的时候，经常会想到使用for循环。

自从 Java 8 引入了 Lambda 后，简化了循环的使用。

举例说明 Lambda的 foreach 和 filter 的简单使用。

 

1、自定义类 Hero

/**
 * Created by Miracle Luna on 2020/3/8
 */
public class Hero {
    private String name;
    private String country;

    public Hero(String name, String country) {
        this.name = name;
        this.country = country;
    }

    public String getName() {
        return name;
    }

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

    public String getCountry() {
        return country;
    }

    public void setCountry(String country) {
        this.country = country;
    }

    @Override
    public String toString() {
        return "Hero{" +
                "name='" + name + '\'' +
                ", country='" + country + '\'' +
                '}';
    }
}

 

2、foreach循环

import java.util.ArrayList;
import java.util.List;

/**
 * Created by Miracle Luna on 2020/3/8
 */
public class LambdaForeachDemo {
    public static void main(String[] args) {
        List<Hero> heroList = new ArrayList<>();
        List<Hero> resultList = new ArrayList<>();

        Hero liubei = new Hero("刘备", "蜀国");
        Hero guanyu = new Hero("关羽", "蜀国");
        Hero zhangfei = new Hero("张飞", "蜀国");
        Hero sunce = new Hero("孙策", "吴国");

        heroList.add(liubei);
        heroList.add(guanyu);
        heroList.add(zhangfei);
        heroList.add(sunce);

        // 查询不是吴国的英雄
        heroList.forEach(hero -> {
            if(!"吴国".equals(hero.getCountry())) {
                resultList.add(hero);
            }
        });

        // 打印结果集合
        resultList.forEach(hero -> System.out.println(hero.toString()));
    }
}

 

3、filter过滤

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

/**
 * Created by Miracle Luna on 2020/3/8
 */
public class LambdaFilterDemo {
    public static void main(String[] args) {
        List<Hero> heroList = new ArrayList<>();
        List<Hero> resultList = new ArrayList<>();

        Hero liubei = new Hero("刘备", "蜀国");
        Hero guanyu = new Hero("关羽", "蜀国");
        Hero zhangfei = new Hero("张飞", "蜀国");
        Hero sunce = new Hero("孙策", "吴国");

        heroList.add(liubei);
        heroList.add(guanyu);
        heroList.add(zhangfei);
        heroList.add(sunce);

        // 查询不是吴国的英雄
        resultList = heroList.stream()
                .filter(hero -> !"吴国".equals(hero.getCountry()))
                .collect(Collectors.toList());

        // 打印结果集合
        resultList.forEach(hero -> System.out.println(hero.toString()));
    }
}

 

4、运行结果如下：

Hero{name='刘备', country='蜀国'}
Hero{name='关羽', country='蜀国'}
Hero{name='张飞', country='蜀国'}