方法引用（Java）

news2024/9/20 22:54:19

把已经有的方法拿过来用，当做函数式接口中抽象方法的方法体

1.引用处必须是函数式接口

2.被引用的方法必须已经存在

3.被引用的方法形参的返回值需要跟抽象方法保持一致

4.被引用方法的功能要满足当前需求

package function;

import java.util.Arrays;

public class FunctionDemo {
    public static void main(String[] args) {
        Integer[] arr = {2, 6, 7, 1, 5, 9, 8};
        Arrays.sort(arr,FunctionDemo::subtraction);
        System.out.println(Arrays.toString(arr));
    }

    public static int subtraction(int num1, int num2) {
        return num2 - num1;
    }
}

方法引用的分类

1.引用静态方法

package function;

import java.util.ArrayList;
import java.util.Collections;


public class FunctionDemo2 {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        Collections.addAll(list,"1","2","3","4","5");
        list.stream().map(Integer::parseInt).forEach(s-> System.out.print(s+" "));
    }
}

2.引用成员方法

①引用其他类的chengyuanfangfa

package function;

import java.util.ArrayList;
import java.util.Collections;

public class FunctionDemo3 {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        Collections.addAll(list,"张三丰","张无忌","张三","张强","韦小宝");
        list.stream().filter(new StringOperation()::stringJudge).forEach(s-> System.out.println(s));
    }
}

package function;

public class StringOperation {
    public boolean stringJudge(String s) {
        return s.startsWith("张") && s.length() == 3;
    }
}

②引用本类的成员方法

静态方法中是没有this的所以只能调用本类的方法

package function;

import java.util.ArrayList;
import java.util.Collections;

public class FunctionDemo3 {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        Collections.addAll(list,"张三丰","张无忌","张三","张强","韦小宝");
//        list.stream().filter(new StringOperation()::stringJudge).forEach(s-> System.out.println(s));
        list.stream().filter(new FunctionDemo3()::stringJudge).forEach(s-> System.out.println(s));
    }
    public boolean stringJudge(String s) {
        return s.startsWith("张") && s.length() == 3;
    }
}

③引用父类的成员方法

3引用构造方法

package function;

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

public class FunctionDemo4 {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        Collections.addAll(list, "张三丰,24", "张无忌,26", "张三,18", "张强,31", "韦小宝,27");
//        list.stream().filter(new StringOperation()::stringJudge).forEach(s-> System.out.println(s));
        List<Student> collect = list.stream().map(Student::new).collect(Collectors.toList());
        System.out.println(collect);
    }
}

package function;

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

    public Student() {
    }

    public Student(String str) {
        String[] split = str.split(",");
        this.name = split[0];
        this.age = Integer.parseInt(split[1]);
    }

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

    /**
     * 获取
     *
     * @return name
     */
    public String getName() {
        return name;
    }

    /**
     * 设置
     *
     * @param name
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * 获取
     *
     * @return age
     */
    public int getAge() {
        return age;
    }

    /**
     * 设置
     *
     * @param age
     */
    public void setAge(int age) {
        this.age = age;
    }

    public String toString() {
        return "Student{name = " + name + ", age = " + age + "}";
    }
}