如何设置命令行输入的条件？ （爪哇）

Question

所以我需要编写一个程序，它有 3 个介于 0 和 255 之间的正整数作为命令行参数（输入），我该如何设置这些条件？到目前为止，我写道：

public class RGBtoCMyk {
public static void main(String []args){
   int r = Integer.parseInt(args[0]);
   int b = Integer.parseInt(args[1]);
   int g = Integer.parseInt(args[2]);

  //now i must set the conditions, that r, g and b are between 0 and 255
  }

如果你有任何想法，请帮助我

Answer 1

您需要处理ArrayIndexOutOfBoundsException 以确保您有足够的输入元素和NumberFormatException 以确保您有int 值。如果您没有这些异常之一，您可以检查所有值是否都在给定的区间内。

public class RGBtoCMyk {
public static void main(String []args){

    try {
    int r = Integer.parseInt(args[0]);
    int b = Integer.parseInt(args[1]);
    int g = Integer.parseInt(args[2]);

    if ((0 <= r) && (r < 256) && (0 <= b) && (b < 256) && (0 <= g) && (g < 256)) {
        System.out.println("Valid colors");
    } else {
        System.out.println("Invalid colors");
    }

    //now i must set the conditions, that r, g and b are between 0 and 255
    } catch (ArrayIndexOutOfBoundsException arrayIndexOutOfBoundsException) {
        System.out.println("Not enough input");
    } catch (NumberFormatException numberFormatException) {
        System.out.println("Inputs are not integer values");
    }
}

Answer 2

您可以添加一个检查条件，如果您的号码超出范围，那么您可以提示用户您可以重新输入。

如果他们输入的值 > 255 并且您想减小它，则没有其他方法。以下是您可以执行的两个选项。

1. 选项 1，如果用户输入超过 255，则将其视为 255，如果值小于零，则将其视为零。万一他输入一个字符串抛出异常。

   public class RGBtoCMyk {
   public static void main(String []args){
   try {
   int r = Integer.parseInt(args[0]);
   int b = Integer.parseInt(args[1]);
   int g = Integer.parseInt(args[2]);
   
   r = r>255 ? 255:r;
   r = r<0 ? 0:r;
   
   g = g>255 ? 255:g;
   g = g<0 ? 0:g;
   
   b = b>255 ? 255:b;
   b = b<0 ? 0:b;
   }
   catch (ArrayIndexOutOfBoundsException arrayIndexOutOfBoundsException) {
   System.out.println("Not enough input");
   } catch (NumberFormatException numberFormatException) {
   System.out.println("Inputs are not integer values");
     }
    }
   }  
   

2. 选项2：如果值不在0到255之间，请再次输入值

   public class RGBtoCMyk {
   public static void main(String []args){
   try {
   Scanner sc=new Scanner(System.in);
   int r = Integer.parseInt(args[0]);
   int b = Integer.parseInt(args[1]);
   int g = Integer.parseInt(args[2]);
   
   If(r>255 || r<0){
   System.out.println("Value Not in Range. Please Enter between 0 and 255");
    int usrInput=sc.nextInt();
    }
   
   //Similarly for g and b.
   b = b>255 ? 255:b;
   b = b<0 ? 0:b;
   }
   
   catch (ArrayIndexOutOfBoundsException arrayIndexOutOfBoundsException) {
   System.out.println("Not enough input");
   } catch (NumberFormatException numberFormatException) {
   System.out.println("Inputs are not integer values");
      }
     }
    }
   

Answer 3

有一些很好的方法可以解析输入数据。

使用说明

如果检测到格式错误的输入，请优雅退出

if(args.length < 3)
{
    printUsage();
    return;
}
int r, g, b;
try
{
    r = Integer.parseInt(args[0]);
    g = Integer.parseInt(args[1]);
    b = Integer.parseInt(args[2]);
}
catch(NumberFormatException e)
{
    printUsage();
    return;
}
if((r | g | b) >> 8 != 0) //same as these other two if statements
//if(((r | g | b) & 0xffffff00) != 0)
//if(r < 0 || r > 255 || g < 0 || g > 255 || b < 0 || b > 255)
{
    printUsage();
    return;
}
//put your code here, you have r, g, and b 0-255

//add in the printUsage method somewhere
public void printUsage()
{
    System.err.println("Input is 3 numbers, each 0-255");
}

引发的错误

这是为了如果您不想捕捉错误并打印出东西，而只是让错误被打印到控制台

int r = Integer.parseInt(args[0]);
int g = Integer.parseInt(args[1]);
int b = Integer.parseInt(args[2]);
//at this point the program will have exited if 3 non-ints were passed, now check values
if((r | g | b) >> 8 != 0) //same as the other two if statements from before
    throw new IllegalArguementException("Color parameters outside of expected range (0-255)"); //mostly copied format from java.awt.Color
//do stuff with r, g, and b being 0-255

处理无效参数

另一种选择是对其进行格式化，以便您可以将 255、0、0 传递为 255

无论您提供什么格式错误的输入，程序都会尝试继续处理

int r = 0;
int g = 0;
int b = 0;
try
{
    r = Integer.parseInt(args[0]);
    g = Integer.parseInt(args[1]);
    b = Integer.parseInt(args[2]);
}
catch(NumberFormatException e){}
if(r >> 8 != 0)
    r = 0;
if(g >> 8 != 0)
    g = 0;
if(b >> 8 != 0)
    b = 0;
//or you could make it so that it takes the last bits, 256 would be 0, 257 would be 1, and so on...
//r = r & 0xFF;
//g = g & 0xFF;
//b = b & 0xFF;

//do stuff with your r, g, and b being 0-255