additionapplet.java

一个用JAVA编写的实现两个浮点数相加的图形界面程序

package chapter3;

// Adding two floatin-point numbers

// java package
import java.awt.Graphics;
import javax.swing.*;

public class AdditionApplet extends JApplet {
	double sum;		// sum of values entered by user
	
	// initialize applet by obtaining values from user
	public void init() {
		String firstNumber;	//first String entered by user
		String secondNumber; // second String entered by user
		
		double number1;		// first number to add 
		double number2;		// second number to add 
		
		// obtain first number from user
		firstNumber = JOptionPane.showInputDialog( 
			"Enter first floating-point value" );
		
		// obtain second number from user
		secondNumber = JOptionPane.showInputDialog(
			"Enter second floating-poing value" );
		
		// covert number2 from type String to type type double
		number1 = Double.parseDouble( firstNumber );
		number2 = Double.parseDouble( secondNumber );
		
		// add number2
		sum = number1 + number2;
		
	} // end method init
	
	// draw results in a rectangle on a applet's background
	public void paint( Graphics g ) {
		// call superclass vetsion of method paint
		super.paint( g );
		
		// drawing rectangle starting from (15, 10) that is 270
		// pixels wide and 20 pixels tall
		g.drawRect( 15, 10, 270, 20 );
		
		// drawing result as a String at (25, 25)
		g.drawString( "The sum is " + sum, 25, 25 );
		
	} // end method paint
	
} // end class AdditionApplet