Java教学资料（华南理工大学）Obtaining Input.pptVIP

Obtaining Input Obtaining Input This book provides three ways of obtaining input. Using JOptionPane input dialogs (§2.15) Using the JDK 1.5 Scanner class (§2.16) Getting Input from Input Dialog Boxes String string = JOptionPane.showInputDialog( null, “Prompting Message”, “Dialog Title”, JOptionPane.QUESTION_MESSAGE)); Two Ways to Invoke the Method There are several ways to use the showInputDialog method. For the time being, you only need to know two ways to invoke it. One is to use a statement as shown in the example: String string = JOptionPane.showInputDialog(null, x, y, JOptionPane.QUESTION_MESSAGE)); where x is a string for the prompting message, and y is a string for the title of the input dialog box. The other is to use a statement like this: JOptionPane.showInputDialog(x); where x is a string for the prompting message. Converting Strings to Integers The input returned from the input dialog box is a string. If you enter a numeric value such as 123, it returns “123”. To obtain the input as a number, you have to convert a string into a number. ? To convert a string into an int value, you can use the static parseInt method in the Integer class as follows: ? int intValue = Integer.parseInt(intString); ? where intString is a numeric string such as “123”. Converting Strings to Doubles To convert a string into a double value, you can use the static parseDouble method in the Double class as follows: ? double doubleValue =Double.parseDouble(doubleString); ? where doubleString is a numeric string such as “123.45”. Example: Computing Loan Payments ComputeLoan Run This program lets the user enter the interest rate, number of years, and loan amount and computes monthly payment and total payment. Example: Monetary Units This program lets the user enter the amount in decimal representing dollars and cents and output a report listing the monetary equivalent in single dollars, quarters, dimes, nickels, and pennies. Your program should report maximum num