Converting Strings to Numbers - Java Tutorial 5.0 英文版

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Converting Strings to Numbers

Sometimes, a program ends up with numeric data in a string object—a value entered by the user, for example. The numeric type-wrapper classes ( Byte, Integer, Double, Float, Long, and Short) each provide a class method named valueOf that converts a string to an object of that type. Here's a small example, ValueOfDemo , that gets two strings from the command line, converts them to numbers, and performs arithmetic operations on the values:

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

	//this program requires two arguments on the command line
        if (args.length == 2) {

            //convert strings to numbers
            float a = Float.valueOf(args[0]).floatValue();
            float b = Float.valueOf(args[1]).floatValue();

            //do some arithmetic
            System.out.println("a + b = " + (a + b) );
            System.out.println("a - b = " + (a - b) );
            System.out.println("a * b = " + (a * b) );
            System.out.println("a / b = " + (a / b) );
            System.out.println("a % b = " + (a % b) );
        } else {
            System.out.println("This program requires two command-line arguments.");
        }
    }
}

The following is the output from the program when you use 4.5 and 87.2 for the command line arguments:

a + b = 91.7
a - b = -82.7
a * b = 392.4
a / b = 0.0516055
a % b = 4.5

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