Q:

(NumberFormatException) Listing 7.9, Calculator.java, is a simple commandline calculator

Nesma
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2022-06-05
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(NumberFormatException) Listing 7.9, Calculator.java, is a simple commandline calculator. Note that the program terminates if any operand is nonnumeric.

Write a program with an exception handler that deals with nonnumeric operands; then write another program without using an exception handler to achieve the same objective. Your program should display a message that informs the user of the wrong operand type before exiting (see Figure 12.12).

FIGURE 12.12 The program performs arithmetic operations and detects input errors.

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Nesma
2022-06-05
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public class CalculatorWithException {
	/** Main method */
	public static void main(String[] args) throws NumberFormatException {
		// Check number of strings passed
		if (args.length != 3) {
			System.out.println(
				"Usage: java Calculator operand1 operator operand2");
			System.exit(0);
		}

		// The result of the operation
		int result = 0;

		// Exeception handler to deal with nonnumeric operands
		try {
			// Determine the operator
			switch (args[1].charAt(0)) {
				case '+' : result = Integer.parseInt(args[0]) +
										  Integer.parseInt(args[2]);
							  break;
				case '-' : result = Integer.parseInt(args[0]) -
										  Integer.parseInt(args[2]);
							  break;
				case '.' : result = Integer.parseInt(args[0]) *
										  Integer.parseInt(args[2]);
							  break;
				case '/' : result = Integer.parseInt(args[0]) /
										  Integer.parseInt(args[2]);
							  break;
			}	

			// Display result
			System.out.println(args[0] + ' ' + args[1] + ' ' + args[2]
				+ " = " + result);
		} 
		catch (NumberFormatException ex) {
			System.out.println("Wrong Input: " + 
				ex.getMessage().substring(ex.getMessage().indexOf(""") + 1, 
					ex.getMessage().lastIndexOf(""")));
		}
	}
}

CalculatorWithoutException.java 

public class CalculatorWithoutException {
	/** Main method */
	public static void main(String[] args) throws Exception {
		// Check number of strings passed
		if (args.length != 3) {
			System.out.println(
				"Usage: java Calculator operand1 operator operand2");
			System.exit(0);
		}
		
		// Test for nonnumeric operands
		testDigit(args[0]);
		testDigit(args[2]);

		// The result of the operation
		int result = 0;

		// Determine the operator
		switch (args[1].charAt(0)) {
			case '+' : result = Integer.parseInt(args[0]) +
									  Integer.parseInt(args[2]);
						  break;
			case '-' : result = Integer.parseInt(args[0]) -
									  Integer.parseInt(args[2]);
						  break;
			case '.' : result = Integer.parseInt(args[0]) *
									  Integer.parseInt(args[2]);
						  break;
			case '/' : result = Integer.parseInt(args[0]) /
									  Integer.parseInt(args[2]);
						  break;
		}

		// Display result
		System.out.println(args[0] + ' ' + args[1] + ' ' + args[2]
			+ " = " + result);
	}

	// Deals with nonnumeric operands
	private static void testDigit(String str) {
		for (int i = 0; i < str.length(); i++) {
			if (!Character.isDigit(str.charAt(i))) {
				System.out.println("Wrong Input: " + str);
				System.exit(0);
			}
		}
	}
}

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