Java基礎系列:Lambda表達式

1 結構

(parameters)->expression
或
(parameters)->{statements;}

2 Usage

• 用到的包

import basic.datatype.po.Infos;
import java.util.List;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.stream.Collectors;
import java.util.Collections;
import java.util.Comparator;
import java.util.Scanner;
import java.util.function.Consumer;
import java.util.Map;

• 實體

package basic.datatype.po;

public class Infos{
    private String name;
    private String address;
    private String score;

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

    public void setAddress(String address){
        this.address = address;
    }
    public String getAddress(){
        return address;
    }

    public void setScore(String score){
        this.score = score;
    }
    public String getScore(){
        return score;
    }
    public Infos(){}
    public Infos(String name, String address, String score){
        this.name = name;
        this.address = address;
        this.score = score;
    }
}

2.1 遍歷列表

public class LambdaExpressionTest implements InterfaceTest{

    public String baseLambda(List datasLis){
        datasLis.forEach(s -> System.out.println(s));
        return "lambda test";
    }
    public static void main(String[] args){
        LambdaExpressionTest lTest = new LambdaExpressionTest();
        List datasLis = Arrays.asList("xiaoxiao", "xiaohei", "xiaohua");
        lTest.baseLambda(datasLis);
    } 
}

其中,s爲datasLis的每個元素,通過forEach遍歷.

2.2 更新數據

package basic.datatype.dataformat;

import basic.datatype.po.Infos;
import java.util.List;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.stream.Collectors;
import java.util.Collections;
import java.util.Comparator;
import java.util.Scanner;
import java.util.function.Consumer;
import java.util.Map;

public class LambdaExpressionTest implements InterfaceTest{

    public List<Infos> infosUpdateByLambda(List<Infos> infosLis){
        Consumer<Infos> updateName = e -> e.setName(e.getName()+"-update");
        infosLis.forEach(updateName);
        return infosLis;
    }
   
    
    public static void main(String[] args){
        LambdaExpressionTest lTest = new LambdaExpressionTest();
        List<Infos> infosLis = new ArrayList<>();
        infosLis.add(new Infos("xiaohua", "shenzhen", "080"));
        infosLis.add(new Infos("xiaoxiao", "shenzhen", "100"));
        infosLis.add(new Infos("xiaohei", "shenzhen", "090"));
        System.out.println("update name:"+lTest.infosUpdateByLambda(infosLis).stream().map(Infos::getName).collect(Collectors.toList()));
    }
}

通過Consumer定義數據接收Lambda修改的變量,forEach進行更新遍歷.

2.3 排序

• 普通排序

package basic.datatype.dataformat;

import basic.datatype.po.Infos;
import java.util.List;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.stream.Collectors;
import java.util.Collections;
import java.util.Comparator;
import java.util.Scanner;
import java.util.function.Consumer;
import java.util.Map;

public class LambdaExpressionTest implements InterfaceTest{

    public List<Infos> sortLiNormal(List<Infos> datasLis){
        Collections.sort(datasLis, new Comparator<Infos>(){
            public int compare(Infos i1, Infos i2){
                return i1.getScore().compareTo(i2.getScore());
            }
        });
        return datasLis;
    }

    public static void main(String[] args){
        LambdaExpressionTest lTest = new LambdaExpressionTest();
        List<Infos> infosLis = new ArrayList<>();
        infosLis.add(new Infos("xiaohua", "shenzhen", "080"));
        infosLis.add(new Infos("xiaoxiao", "shenzhen", "100"));
        infosLis.add(new Infos("xiaohei", "shenzhen", "090"));   
        System.out.println("sort normal:"+lTest.sortLiNormal(infosLis).stream().map(Infos::getScore).collect(Collectors.toList()));
    }  
}

• Lambda排序

package basic.datatype.dataformat;

import basic.datatype.po.Infos;
import java.util.List;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.stream.Collectors;
import java.util.Collections;
import java.util.Comparator;
import java.util.Scanner;
import java.util.function.Consumer;
import java.util.Map;

public class LambdaExpressionTest implements InterfaceTest{

    public List<Infos> sortLiNormal(List<Infos> datasLis){
        Collections.sort(datasLis, new Comparator<Infos>(){
            public int compare(Infos i1, Infos i2){
                return i1.getScore().compareTo(i2.getScore());
            }
        });
        return datasLis;
    }

    public static void main(String[] args){
        LambdaExpressionTest lTest = new LambdaExpressionTest();
        List<Infos> infosLis = new ArrayList<>();
        infosLis.add(new Infos("xiaohua", "shenzhen", "080"));
        infosLis.add(new Infos("xiaoxiao", "shenzhen", "100"));
        infosLis.add(new Infos("xiaohei", "shenzhen", "090"));   
        System.out.println("sort by lambda:"+lTest.sortLiByLambda(infosLis).stream().map(Infos::getScore).collect(Collectors.toList()));
    }  
}

---

【參考文獻】
[1]https://www.cnblogs.com/coprince/p/8692972.html
[2]https://blog.csdn.net/qq_37176126/article/details/81273195
[3]https://www.jianshu.com/p/a01d84c57180
[4]https://blog.csdn.net/weixin_37766087/article/details/94999833