编写一个java程序，从键盘输入一个x值，程序输出一个y值

非常抱歉，请您详细描述一下，x值和y值的来历。程序内部需要执行什么样的命令，来将x值变成y值，肯定需要写函数。

f(x)= x+1;这样也是一个函数。

还是只要写一个输入x,输出y,就好了。

输入

import java.util.Scanner;

public class Main {
    public static void main(String args[]){
        Scanner scanner = new Scanner(System.in);
        System.out.println("Input x:");
        Integer x = scanner.nextInt();
        Integer y =0;
        if(x<0){
            y = -1+2*x;
        }else{
            y = -1+3*x;
        }



        System.out.println("Output y:"+y);
    }
}

输出

"C:\Program Files\Java\jdk1.8.0_201\bin\java.exe" "-javaagent:D:\IntelliJ IDEA 2020.3\lib\idea_rt.jar=55416:D:\IntelliJ IDEA 2020.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_201\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\rt.jar;C:\Users\38684\IdeaProjects\title\out\production\title" Main
Input x:
2
Output y:3

Process finished with exit code 0

"C:\Program Files\Java\jdk1.8.0_201\bin\java.exe" "-javaagent:D:\IntelliJ IDEA 2020.3\lib\idea_rt.jar=55452:D:\IntelliJ IDEA 2020.3\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_201\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_201\jre\lib\rt.jar;C:\Users\38684\IdeaProjects\title\out\production\title" Main
Input x:
0
Output y:-1

Process finished with exit code 0

应该有一个表达式吧

package com.auskat.demo.lock;

import java.util.*;

/**
 * 类文件: ScannerDemo
 * <p>
 * <p>
 * 类描述：
 * <p>
 * 作     者： AusKa_T
 * <p>
 * 日     期： 2021/5/16 0016
 * <p>
 * 时     间： 15:51
 * <p>
 */
public class ScannerDemo {


    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入X的值：");
        String xString = sc.next();
        int x = Integer.parseInt(xString);
        Integer y = 0;
        if (x < 0) {
            y = -1 + 2 * x;
        } else if (x == 0) {
            y = -1;
        } else {
            y = -1 + 3 * x;
        }
        System.out.println(y);
        sc.close();
    }
}

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