Java 8:Lambda表达式包含多个语句/逻辑

Question

我写了一个简单的程序来迭代List使用java 8 lambda.

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;

public class FirstLamdaExpression {

    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
        //Way 1 : old way
        list.forEach(new Consumer<Integer>() {

            @Override
            public void accept(Integer t) {
                System.out.print(t + " ");

            }
        });

        //Way 2
        System.out.println(" ");
        list.forEach((Integer t) -> System.out.print(t + " "));

        //Way 3
        System.out.println(" ");
        list.forEach((t) -> System.out.print(t + " "));

        //Way 4
        System.out.println(" ");
        list.forEach(System.out::print);

    }

}

在下面的程序中,我在lambda中执行了两个以上的逻辑.我面临的问题是如何更新第四种方式即System.out::print？

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;

public class SecondLamdaExpression {

    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
        //Way 1 : Old way
        list.forEach(new Consumer<Integer>() {

            @Override
            public void accept(Integer t) {
                System.out.print(t + "  Twice is : ");
                System.out.print(t*2 + "  , ");

            }
        });

        //Way 2
        System.out.println(" ");
        list.forEach((Integer t) -> 
             {System.out.print(t + "  Twice is : ");
                System.out.print(t*2 + "  , ");
             });

        //Way 3
        System.out.println(" ");
        list.forEach((t) ->  {System.out.print(t + "  Twice is : ");
        System.out.print(t*2 + "  , ");
         });

        //Way 4
        //System.out.println(" ");
        //list.forEach((t)-> System.out::print{(t + "  Twice is : ");});

    }

}

Answer 1

看来你问的是如何传递t + " Twice is : " + t*2 + " , "给方法引用.您不能将显式参数传递给方法引用,也不能将方法引用与lambda表达式组合在一起.

您可以使用Stream管道首先map t为每个值打印任何内容t,然后使用forEachwith方法引用来打印它:

list.stream().map(t -> t + "  Twice is : " + t*2 + "  , ").forEach(System.out::print);