Java 8 : Lambda expression contains more than one statement/logic

Question

我编写了一个简单的程序来使用 java 8 lambda 遍历 List。

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，我有 2 个以上的逻辑要在 lambda 中执行。我面临的问题是如何更新第 4 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

您似乎在问如何将 t + "Twice is : "+ t*2 + ", " 传递给方法引用。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 表达式结合使用。

您可以使用 Stream 管道首先 map t 您希望为 t 的每个值打印任何内容>，然后使用带有方法引用的 forEach 来打印它:

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