Exercise Arithmetic (Command-line arguments): Write a program called Arithmetic that takes three command-line arguments: two integers followed by an arithmetic operator (+, -, * or /). The program shall perform the corresponding operation on the two integers and print the result. For example: java Arithmetic 3 2 + 3+2=5    java Arithmetic 3 2 - 3-2=1    java Arithmetic 3 2 / 3/2=1 Hints: The method main(String[] args) takes an argument: "an array of String", which is often (but not necessary) named args. This parameter captures the command-line arguments supplied by the user when the program is invoked. For example, if a user invokes: java Arithmetic 12345 4567 + The three command-line arguments "12345", "4567" and "+" will be captured in a String array {"12345", "4567", "+"} and passed into the main() method as the argument args. That is, args is: {"12345", "4567", "+"}  // args is a String array args.length is: 3                // length of the array args[0] is: "12345"              // 1st element of the String array args[1] is: "4567"               // 2nd element of the String array args[2] is: "+"                  // 3rd element of the String array args[0].length() is: 5           // length of 1st String element args[1].length() is: 4           // length of the 2nd String element args[2].length() is: 1           // length of the 3rd String element public class Arithmetic {   public static void main (String[] args) {     int operand1, operand2;     char theOperator;       // Check if there are 3 command-line arguments in the     //  String array args[] by using length variable of array.     if (args.length != 3) {       System.err.println("Usage: java Arithmetic int1 int2 op");       return;     }        // Convert the 3 Strings args[0], args[1], args[2] to int and char.     // Use the Integer.parseInt(aStr) to convert a String to an int.     operand1 = Integer.parseInt(args[0]);     operand2 = ......        // Get the operator, assumed to be the first character of     //  the 3rd string. Use method charAt() of String.     theOperator = args[2].charAt(0);     System.out.print(args[0] + args[2] + args[1] + "=");        switch(theOperator) {       case ('-'): System.out.println(operand1 - operand2); break;       case ('+'): ......       case ('*'): ......       case ('/'): ......       default:         System.err.println("Error: invalid operator!");     }   } } Notes: To provide command-line arguments, use the "cmd" or "terminal" to run your program in the form "java ClassName arg1 arg2 ....". To provide command-line arguments in Eclipse, right click the source code ⇒ "Run As" ⇒ "Run Configurations..." ⇒ Select "Main" and choose the proper main class ⇒ Select "Arguments" ⇒ Enter the command-line arguments, e.g., "3 2 +" in "Program Arguments". To provide command-line arguments in NetBeans, right click the "Project" name ⇒ "Set Configuration" ⇒ "Customize..." ⇒ Select categories "Run" ⇒ Enter the command-line arguments, e.g., "3 2 +" in the "Arguments" box (but make sure you select the proper Main class). Question: Try "java Arithmetic 2 4 *" (in CMD shell and Eclipse/NetBeans) and explain the result obtained. How to resolve this problem? In Windows' CMD shell, * is known as a wildcard character, that expands to give the list of file in the directory (called Shell Expansion). For example, "dir *.java" lists all the file with extension of ".java". You could double-quote the * to prevent shell expansion. Eclipse has a bug in handling this, even * is double-quoted. NetBeans?? Exercise SumDigits (Command-line arguments): Write a program called SumDigits to sum up the individual digits of a positive integer, given in the command line. The output shall look like: java SumDigits 12345 The sum of digits = 1 + 2 + 3 + 4 + 5 = 15

Exercise Arithmetic (Command-line arguments): Write a program called Arithmetic that takes three command-line arguments: two integers followed by an arithmetic operator (+, -, * or /). The program shall perform the corresponding operation on the two integers and print the result. For example:

java Arithmetic 3 2 +

3+2=5

java Arithmetic 3 2 -

3-2=1

java Arithmetic 3 2 /

3/2=1

Hints:

The method main(String[] args) takes an argument: "an array of String", which is often (but not necessary) named args. This parameter captures the command-line arguments supplied by the user when the program is invoked. For example, if a user invokes:

java Arithmetic 12345 4567 +

The three command-line arguments "12345", "4567" and "+" will be captured in a String array {"12345", "4567", "+"} and passed into the main() method as the argument args. That is,

args is: {"12345", "4567", "+"}  // args is a String array

args.length is: 3                // length of the array

args[0] is: "12345"              // 1st element of the String array

args[1] is: "4567"               // 2nd element of the String array

args[2] is: "+"                  // 3rd element of the String array

args[0].length() is: 5           // length of 1st String element

args[1].length() is: 4           // length of the 2nd String element

args[2].length() is: 1           // length of the 3rd String element

public class Arithmetic {

  public static void main (String[] args) {

    int operand1, operand2;

    char theOperator;

    // Check if there are 3 command-line arguments in the

    //  String array args[] by using length variable of array.

    if (args.length != 3) {

      System.err.println("Usage: java Arithmetic int1 int2 op");

      return;

    }

    // Convert the 3 Strings args[0], args[1], args[2] to int and char.

    // Use the Integer.parseInt(aStr) to convert a String to an int.

    operand1 = Integer.parseInt(args[0]);

    operand2 = ......

    // Get the operator, assumed to be the first character of

    //  the 3rd string. Use method charAt() of String.

    theOperator = args[2].charAt(0);

    System.out.print(args[0] + args[2] + args[1] + "=");

    switch(theOperator) {

      case ('-'): System.out.println(operand1 - operand2); break;

      case ('+'): ......

      case ('*'): ......

      case ('/'): ......

      default:

        System.err.println("Error: invalid operator!");

    }

  }

}

Notes:

• To provide command-line arguments, use the "cmd" or "terminal" to run your program in the form "java ClassName arg1 arg2 ....".
• To provide command-line arguments in Eclipse, right click the source code ⇒ "Run As" ⇒ "Run Configurations..." ⇒ Select "Main" and choose the proper main class ⇒ Select "Arguments" ⇒ Enter the command-line arguments, e.g., "3 2 +" in "Program Arguments".
• To provide command-line arguments in NetBeans, right click the "Project" name ⇒ "Set Configuration" ⇒ "Customize..." ⇒ Select categories "Run" ⇒ Enter the command-line arguments, e.g., "3 2 +" in the "Arguments" box (but make sure you select the proper Main class).

Question: Try "java Arithmetic 2 4 *" (in CMD shell and Eclipse/NetBeans) and explain the result obtained. How to resolve this problem?

In Windows' CMD shell, * is known as a wildcard character, that expands to give the list of file in the directory (called Shell Expansion). For example, "dir *.java" lists all the file with extension of ".java". You could double-quote the * to prevent shell expansion. Eclipse has a bug in handling this, even * is double-quoted. NetBeans??

Exercise SumDigits (Command-line arguments): Write a program called SumDigits to sum up the individual digits of a positive integer, given in the command line. The output shall look like:

java SumDigits 12345

The sum of digits = 1 + 2 + 3 + 4 + 5 = 15