Java中双冒号::的作用举例详解

import org.junit.Test;
import java.util.Arrays;
import java.util.List;

public class Colon{
@Test
    public void test(){
        List<String> list = Arrays.asList("a", "b","c");
        //静态方法引用ClassName::methodName
        list.forEach(Colon:: print);
        //上一行等价于
        //1ist.forEach((x)->Colon.print(x));
    }
    //静态方法
    public static void print(String s){
        system.out.println(s);
    }
}

import org.junit.Test;
import java.util.Arrays;
import java.util.List;
public class Colon{
    @Test
    public void test(){
        List<string> list = Arrays.asList("a", "b","c");//r实例方法引用instanceRef: :methodName
        list.forEach(new Colon()::print);
        //上一行等价于
        //iist.forEach((x)->new Colon().print(x));
    }
    //实例方法
    public void print(String s){
        System.out.println(s);
    }
}

import org.junit.Test;
import java.util.Arrays;

public class Colon{
    @Test
    public void test(){
        String[] arr = { "Barbara","James","Mary", "John",
                "Patricia","Robert","Michae1", "Linda”};
        //引用String类型的任意对象的compareToIgnoreCase方法实现忽略大小写排序
        Arrays.sort(arr, String::compareToIgnoreCase);
        //上一行等价于
        //Arrays.sort(arr, (a,b)->a.compareToIgnoreCase(b));
        //输出
        for(String s:arr){
            System.out.println(s);
        }
}

import org.junit.Test;
import java.util.Arrays;
import java.util.List;

public class Colon extends BaseColon{
    @Test
    public void test(){
        List<string> list = Arrays.asList("a", "b","c");
        //实例方法引用instanceRef::methodName
        list.forEach(super:: print);
    }
}
class Basecolon{
    //实例方法
    public void print(string s){
        System.out.println(s);
    }
}

//注意:该类无需实现接口
public class Colon{
    private String name;
    private int age;
    //无参构造
    public Colon(){ }
    //有参构造
    public colon(String name, int age){
        this.name = name;
        this.age = age;
    }
    public static void main(String[] args){
        //无参构造引用
        ColonNoParam cnp = Colon::new;
        colon c1 = cnp.createColon();
        System.out.println(c1);
        //有参构造引用
        ColonlithParam cwp = Colon::new;
        colon c2 = cwp.createColon("小明",20);
        System.out.println(c2);
    }
    //生成toString方法打印查看
    @Override
    public string toString() {
        return "Colon{" +
                "name='"+ name + "\"+
                ",age=" + age +
                '}';
    }
}
interface colonNoParam{
    //无参方法提供对象
    Colon createColon();
}
interface ColonwithParam{
    //有参方法提供对象（数据类型要与colon有参构造函数对应)
    colon createColon(String s,int i);
}

public class Colon{
    public static void main(string[] args) {
        MyArrayFunction<Integer,Colon[]> function = Colon[]::new;
        //调用apply方法创建数组,这里的5是教组的长度
        colon[] arr = function.apply(5);
        //循环输出-初始都为null
        for(Colon c:arr){
            System.out.println(c);
        }
    }
}
//自定义函教式接口
@FunctionalInterface
interface MyArrayFunction<A,T>{
    T apply(A a);
}