Java函數(shù)式Lambda編程的使用學(xué)習(xí)（圖文教程）

更新時(shí)間：2025年11月08日 14:05:16 作者：Mason_studying

文章介紹了Java中的Lambda表達(dá)式,它是一種替代匿名內(nèi)部類的簡(jiǎn)潔方式,適用于函數(shù)式接口,通過(guò)Lambda表達(dá)式,可以簡(jiǎn)化代碼,提高可讀性,文章還討論了方法引用的幾種常見(jiàn)用法,包括靜態(tài)方法引用、實(shí)例方法引用、特定類型方法引用和構(gòu)造器引用

1.Lambda表達(dá)式

1.1 定義

JDK 8開(kāi)始新增的一種語(yǔ)法形式，它表示函數(shù)
可以用于替代某些匿名內(nèi)部類，從而讓程序更簡(jiǎn)潔，可讀性更好

Tips:Lambda表達(dá)式只能替代函數(shù)式接口的匿名內(nèi)部類

（被重寫(xiě)方法的形參列表）->
{
	被重寫(xiě)方法的方法體代碼
}

函數(shù)式接口：

有且僅有一個(gè)抽象方法的接口
注意：將來(lái)見(jiàn)到的大部分函數(shù)式接口，上面都可能會(huì)有一個(gè)@FunctionalInterface的注解，該注解用于約束當(dāng)前接口必須是函數(shù)式接口

public class Lambdademo {
    public static void main(String[] args) {
        Animal a = new Animal() {
            @Override
            public void eat() {
                System.out.println("狗吃骨頭");
            }
        };
        a.eat();


        System.out.println("============================");
        Swim s1=new Swim() {
            @Override
            public void swim() {
                System.out.println("學(xué)生游泳賊快");
            }
        }

        Swim s2=()->{
            System.out.println("學(xué)生游泳賊快");
        }
    }

}
abstract class Animal{
    abstract void eat();
}

//函數(shù)式接口:有且僅有一個(gè)抽象方法的接口
@FunctionalInterface//聲明函數(shù)式接口的注解
interface Swim{
    void swim();
}

分析這段代碼：

Animal由于只是抽象類不是接口，所以不能使用Lambda表達(dá)式替代

而Swim是接口，且只有一個(gè)抽象方法所以能被Lambda表達(dá)式替代

**為什么這個(gè)Lambda能替代？**因?yàn)槟芡茢喑錾舷挛模琒wim s2能推斷出是一個(gè)接口，后面的方法體代碼能代碼能推斷出只有一個(gè)抽象方法，所以能推斷出原來(lái)的代碼如s1。

1.2 實(shí)例

1.2.1 用comparator接口的匿名內(nèi)部函數(shù)類實(shí)現(xiàn)對(duì)數(shù)組進(jìn)行排序

在匿名內(nèi)部類中使用comparator接口的匿名內(nèi)部函數(shù)類實(shí)現(xiàn)對(duì)數(shù)組進(jìn)行排序代碼中可以看到編譯器用灰色標(biāo)記Comparator提示可以進(jìn)行Lambda表達(dá)式進(jìn)行簡(jiǎn)化，進(jìn)入該方法的聲明，該方法有聲明函數(shù)式接口的注解，說(shuō)明該匿名內(nèi)部類可以使用Lambda表達(dá)式進(jìn)行化簡(jiǎn)

import com.fqw.anonymousclass.Student;

import java.util.Arrays;
import java.util.Comparator;

public class Lambdademo1 {
    public static void main(String[] args) {
        Student[] students=new Student[6];
        students[0]=new Student("張三", 18, 1.75);
        students[1]=new Student("李四", 23, 1.80);
        students[2]=new Student("王五", 20, 1.65);
        students[3]=new Student("趙六", 17, 1.70);
        students[4]=new Student("錢七", 22, 1.65);
        students[5]=new Student("孫八", 16, 1.75);
        //輸出排序前的學(xué)生數(shù)組
        for (int i=0;i<students.length;i++){
            Student student = students[i];
            System.out.println(student.getName()+","+ student.getAge()+","+ student.getHeight());
        }


        Arrays.sort(students, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2)
            {
                return o1.getAge()-o2.getAge();//升序

            }
        });
        System.out.println("=======================================");
        //輸出排序后的學(xué)生數(shù)組
        for (int i=0;i<students.length;i++){
            Student student = students[i];
            System.out.println(student.getName()+","+ student.getAge()+","+ student.getHeight());
        }

    }
}

簡(jiǎn)化后的代碼

import com.fqw.anonymousclass.Student;

import java.util.Arrays;
import java.util.Comparator;

public class Lambdademo1 {
    public static void main(String[] args) {
        Student[] students=new Student[6];
        students[0]=new Student("張三", 18, 1.75);
        students[1]=new Student("李四", 23, 1.80);
        students[2]=new Student("王五", 20, 1.65);
        students[3]=new Student("趙六", 17, 1.70);
        students[4]=new Student("錢七", 22, 1.65);
        students[5]=new Student("孫八", 16, 1.75);
        //輸出排序前的學(xué)生數(shù)組
        for (int i=0;i<students.length;i++){
            Student student = students[i];
            System.out.println(student.getName()+","+ student.getAge()+","+ student.getHeight());
        }


        Arrays.sort(students, (Student o1, Student o2)->{
                return o1.getAge()-o2.getAge();//升序

        });
        System.out.println("=======================================");
        //輸出排序后的學(xué)生數(shù)組
        for (int i=0;i<students.length;i++){
            Student student = students[i];
            System.out.println(student.getName()+","+ student.getAge()+","+ student.getHeight());
        }

    }
}

1.2.2 登錄窗口登錄

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Lambdademo2 {
    public static void main(String[] args) {
        //需求：創(chuàng)建一個(gè)登錄窗口，登錄窗口中包含一個(gè)登錄按鈕
        JFrame win = new JFrame("登錄窗口");
        win.setSize(300, 200);
        win.setLocationRelativeTo(null);//居中顯示
        win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //創(chuàng)建一個(gè)面板，把按鈕添加到面板中
        JPanel panel = new JPanel();
        win.add(panel);

        //創(chuàng)建一個(gè)按鈕
        JButton button = new JButton("登錄");
        panel.add(button);

        //java要求必須給按鈕添加一個(gè)點(diǎn)擊事件監(jiān)聽(tīng)器對(duì)象，這樣就可以監(jiān)聽(tīng)用戶事件，做出反應(yīng)
        button.addActionListener((ActionEvent e) -> {
                System.out.println("登錄成功");
        });


        win.setVisible(true);


    }
}

1.3 省略規(guī)則(進(jìn)一步簡(jiǎn)化Lambda表達(dá)式的寫(xiě)法)

參數(shù)類型全部可以省略不寫(xiě)
如果只有一個(gè)參數(shù)，參數(shù)類型省略的同時(shí)“()”也可以省略，但多個(gè)參數(shù)不能省略“()”
如果Lambda表達(dá)式只有一行代碼，大括號(hào)可以不寫(xiě)，同時(shí)要省略分號(hào)”;”，如果這行代碼是return語(yǔ)句，也必須去掉return

根據(jù)簡(jiǎn)化規(guī)則簡(jiǎn)化后的代碼：

import com.fqw.anonymousclass.Student;

import java.util.Arrays;
import java.util.Comparator;

public class Lambdademo1 {
    public static void main(String[] args) {
        Student[] students=new Student[6];
        students[0]=new Student("張三", 18, 1.75);
        students[1]=new Student("李四", 23, 1.80);
        students[2]=new Student("王五", 20, 1.65);
        students[3]=new Student("趙六", 17, 1.70);
        students[4]=new Student("錢七", 22, 1.65);
        students[5]=new Student("孫八", 16, 1.75);
        //輸出排序前的學(xué)生數(shù)組
        for (int i=0;i<students.length;i++){
            Student student = students[i];
            System.out.println(student.getName()+","+ student.getAge()+","+ student.getHeight());
        }


        Arrays.sort(students, ( o1,  o2) -> o1.getAge()-o2.getAge());
        System.out.println("=======================================");
        //輸出排序后的學(xué)生數(shù)組
        for (int i=0;i<students.length;i++){
            Student student = students[i];
            System.out.println(student.getName()+","+ student.getAge()+","+ student.getHeight());
        }

    }
}

import javax.swing.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Lambdademo2 {
    public static void main(String[] args) {
        //需求：創(chuàng)建一個(gè)登錄窗口，登錄窗口中包含一個(gè)登錄按鈕
        JFrame win = new JFrame("登錄窗口");
        win.setSize(300, 200);
        win.setLocationRelativeTo(null);//居中顯示
        win.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //創(chuàng)建一個(gè)面板，把按鈕添加到面板中
        JPanel panel = new JPanel();
        win.add(panel);

        //創(chuàng)建一個(gè)按鈕
        JButton button = new JButton("登錄");
        panel.add(button);

        //java要求必須給按鈕添加一個(gè)點(diǎn)擊事件監(jiān)聽(tīng)器對(duì)象，這樣就可以監(jiān)聽(tīng)用戶事件，做出反應(yīng)
        button.addActionListener(e -> System.out.println("登錄成功"));


        win.setVisible(true);


    }
}

2.方法引用（了解）

2.1 靜態(tài)方法引用

類名::靜態(tài)方法

使用場(chǎng)景：如果某個(gè)Lambda表達(dá)式里只調(diào)用一個(gè)靜態(tài)方法，并且“->”前后參數(shù)的形式一致，就可以使用靜態(tài)方法

1.首先，在類中定義一個(gè)靜態(tài)的方法，如學(xué)生類中定義一個(gè)比較年齡的靜態(tài)類

package com.fqw.method1reference;

public class Student {
    //姓名、年齡、身高
    private String name;
    private int age;
    private double height;
    public Student() {}
    public Student(String name, int age, double height) {
        this.name = name;
        this.age = age;
        this.height = height;
    }

    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;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    public static int compareAge(Student s1, Student s2){
        return s1.getAge() - s2.getAge();
    }
}

2.接著，使用靜態(tài)方法引用

package com.fqw.method1reference;

import java.util.Arrays;

public class Demo1{
    public static void main(String[] args) {
        Student[] students=new Student[6];
        students[0]=new Student("張三", 18, 1.75);
        students[1]=new Student("李四", 23, 1.80);
        students[2]=new Student("王五", 20, 1.65);
        students[3]=new Student("趙六", 17, 1.70);
        students[4]=new Student("錢七", 22, 1.65);
        students[5]=new Student("孫八", 16, 1.75);
        //輸出排序前的學(xué)生數(shù)組
        for (int i=0;i<students.length;i++){
            Student student = students[i];
            System.out.println(student.getName()+","+ student.getAge()+","+ student.getHeight());
        }
        //Arrays.sort(students, ( o1,  o2) -> o1.getAge()-o2.getAge);
        //Arrays.sort(students, ( o1,  o2) -> Student.compareAge(o1,o2));
        //靜態(tài)方法引用 類名::靜態(tài)方法
        Arrays.sort(students, Student::compareAge);
        System.out.println("=======================================");
        //輸出排序后的學(xué)生數(shù)組
        for (int i=0;i<students.length;i++){
            Student student = students[i];
            System.out.println(student.getName()+","+ student.getAge()+","+ student.getHeight());
        }
    }

}

2.2 實(shí)例方法引用

對(duì)象名::實(shí)例方法

使用場(chǎng)景：如果某個(gè)Lambda表達(dá)式里只是通過(guò)對(duì)象名稱調(diào)用一個(gè)實(shí)例方法，并且“->”前后參數(shù)的形式一致，就可以使用實(shí)例方法

package com.fqw.method1reference;

public class Student {
    //姓名、年齡、身高
    private String name;
    private int age;
    private double height;
    public Student() {}
    public Student(String name, int age, double height) {
        this.name = name;
        this.age = age;
        this.height = height;
    }

    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;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }


    

    public int compareByHeight(Student o1,Student o2){
        return Double.compare(o1.getHeight(), o2.getHeight());
    }
}

package com.fqw.method1reference;

import java.util.Arrays;

public class Demo2 {
    public static void main(String[] args) {
        Student[] students=new Student[6];
        students[0]=new Student("張三", 18, 1.75);
        students[1]=new Student("李四", 23, 1.80);
        students[2]=new Student("王五", 20, 1.65);
        students[3]=new Student("趙六", 17, 1.70);
        students[4]=new Student("錢七", 22, 1.65);
        students[5]=new Student("孫八", 16, 1.75);
        //輸出排序前的學(xué)生數(shù)組
        for (int i=0;i<students.length;i++){
            Student student = students[i];
            System.out.println(student.getName()+","+ student.getAge()+","+ student.getHeight());
        }


        //實(shí)例方法引用 對(duì)象名::靜態(tài)方法
        Student t=new Student();
        //Arrays.sort(students, ( o1,  o2) -> t.compareByHeight(o1,o2));
        Arrays.sort(students, t::compareByHeight);
        System.out.println("=======================================");
        //輸出排序后的學(xué)生數(shù)組
        for (int i=0;i<students.length;i++){
            Student student = students[i];
            System.out.println(student.getName()+","+ student.getAge()+","+ student.getHeight());
        }
    }
}

2.3 特定類型方法的引用

特定類的名稱::方法

使用場(chǎng)景：如果某個(gè)Lambda表達(dá)式里只調(diào)用一個(gè)特定類型的實(shí)例方法，并且前面參數(shù)列表中的第一個(gè)參數(shù)是作為方法的主調(diào)，后面的所有參數(shù)都是作為該實(shí)例方法的入?yún)⒌模瑒t此時(shí)就可以使用特定類型的方法引用

場(chǎng)景：有一個(gè)字符串?dāng)?shù)組，里面有一些人的名字，都是英文名字，請(qǐng)按照名字的英文首字母排序,忽略首字母大小

import java.util.Arrays;
import java.util.Comparator;

public class Demo3 {
    public static void main(String[] args) {
        //有一個(gè)字符串?dāng)?shù)組，里面有一些人的名字，都是英文名字，請(qǐng)按照名字的英文首字母排序,忽略首字母大小
        String[] names=new String[]{"Tom","lisi","angela","zhaoliu","Mike","Jack","Bob","Andy","caocao","Rose"};
//        Arrays.sort(names, new Comparator<String>() {
//            @Override
//            public int compare(String o1, String o2) {
//                return o1.compareToIgnoreCase(o2);
//            }
//        });
        //Arrays.sort(names, (o1,o2)->o1.compareToIgnoreCase(o2));
        Arrays.sort(names, String::compareToIgnoreCase);

        System.out.println(Arrays.toString(names));
    }
}

2.4 構(gòu)造器引用

類名::new

使用場(chǎng)景：如果某個(gè)Lambda表達(dá)式里只是創(chuàng)建對(duì)象，并且“->”前后參數(shù)的形式一致，就可以使用構(gòu)造器引用

package com.fqw.method1reference;

public class Demo4 {
    public static void main(String[] args) {
//        CarFactory cf=new CarFactory() {
//            @Override
//            public Car getCar(String name){
//                return new Car(name);
//            }
//        };
//        CarFactory cf=name ->  new Car(name);

        CarFactory cf=Car:: new ;
        Car c1=cf.getCar("奧迪");
        System.out.println(c1.getName());

    }
}

interface CarFactory{
    Car getCar(String name);
}

class Car{
    private String name;

    public Car() {
    }

    public Car(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

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

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