Addition.java
两数相加
源代码：
// An addition program
import javax.swing.JOptionPane; // import class JOptionPane
public class Addition {
public static void main( String args[] )
{
String firstNumber, // first string entered by user
secondNumber; // second string entered by user
int number1, // first number to add
number2, // second number to add
sum; // sum of number1 and number2
// read in first number from user as a string
firstNumber =
JOptionPane.showInputDialog( "Enter first integer" );
// read in second number from user as a string
secondNumber =
JOptionPane.showInputDialog( "Enter second integer" );
// convert numbers from type String to type int
number1 = Integer.parseInt( firstNumber );
number2 = Integer.parseInt( secondNumber );
// add the numbers
sum = number1 + number2;
// display the results
JOptionPane.showMessageDialog(
null, "The sum is " + sum, "Results",
JOptionPane.PLAIN_MESSAGE );
System.exit( 0 ); // terminate the program
}
}
感悟：通过弹出对话框的形式先后输入两个数并最后计算两数之和。。
Text Double.Java
源代码：
package 双精度;
public class TestDouble {
public static void main(String args[]) {
System.out.println("0.05+0.01="+(0.05+0.01));
System.out.println("1.0-0.42="+(1.0-0.42));
System.out.println("4.015*100="+(4.015*100));
System.out.println("123.3/100"+(123.3/100));
}
}
感悟：双精度直接使用会产生误差；
EnumTest.java
源代码：
public class EnumTest {
public static void main(String[] args) {
Size s=Size.SMALL;
Size t=Size.LARGE;
//s和t引用同一个对象？
System.out.println(s==t); //
//是原始数据类型吗？
System.out.println(s.getClass().isPrimitive());
//从字符串中转换
Size u=Size.valueOf("SMALL");
System.out.println(s==u); //true
//列出它的所有值
for(Size value:Size.values()){
System.out.println(value);
}
}
}
enum Size{SMALL,MEDIUM,LARGE};
感悟：
InputTest.java
/**
@version 1.10 2004-02-10
@author Cay Horstmann
*/
import java.util.*;
public class InputTest
{
public static void main(String[] args)
{
Scanner in = new Scanner(System.in);
// get first input
System.out.print("What is your name? ");
String name = in.nextLine();
// get second input
System.out.print("How old are you? ");
int age = in.nextInt();
/* int i;
String value="100";
i=Integer.parseInt(value);
i=200;
String s=String.valueOf(i);*/
// display output on console
System.out.println("Hello, " + name + ". Next year, you'll be " + (age + 1));
}
}
感悟：
通过对话框的弹出先输入姓名年龄最后输出明年此人的年龄；
RandomTest.java
源代码：
public class RandomStr
{
public static void main(String[] args)
{
//定义一个空字符串
String result = "";
//进行6次循环
for(int i = 0 ; i < 6 ; i ++)
{
//生成一个97～122的int型的整数
int intVal = (int)(Math.random() * 26 + 97);
//将intValue强制转换为char后连接到result后面
result = result + (char)intVal;
}
//输出随机字符串
System.out.println(result);
}
}
感悟：通过循环产生随机数，强制转化类型产生随机的六位小写字母；
SwitchTest.java
源代码：
// Drawing shapes
import java.awt.Graphics;
import javax.swing.*;
public class SwitchTest extends JApplet {
int choice;
public void init()
{
String input;
input = JOptionPane.showInputDialog(
"Enter 1 to draw lines " +
"Enter 2 to draw rectangles " +
"Enter 3 to draw ovals " );
choice = Integer.parseInt( input );
}
public void paint( Graphics g )
{
for ( int i = 0; i < 10; i++ ) {
switch( choice ) {
case 1:
g.drawLine( 10, 10, 250, 10 + i * 10 );
break;
case 2:
g.drawRect( 10 + i * 10, 10 + i * 10,
50 + i * 10, 50 + i * 10 );
break;
case 3:
g.drawOval( 10 + i * 10, 10 + i * 10,
50 + i * 10, 50 + i * 10 );
break;
default:
JOptionPane.showMessageDialog(
null, "Invalid value entered" );
} // end switch
} // end for
} // end paint()
} // end class SwitchTest
/**************************************************************************
* (C) Copyright 1999 by Deitel & Associates, Inc. and Prentice Hall. *
* All Rights Reserved. *
* *
* DISCLAIMER: The authors and publisher of this book have used their *
* best efforts in preparing the book. These efforts include the *
* development, research, and testing of the theories and programs *
* to determine their effectiveness. The authors and publisher make *
* no warranty of any kind, expressed or implied, with regard to these *
* programs or to the documentation contained in these books. The authors *
* and publisher shall not be liable in any event for incidental or *
* consequential damages in connection with, or arising out of, the *
* furnishing, performance, or use of these programs. *
*************************************************************************/
运行截图：
Test.java
源代码：
public class Test {
public static void main(String[] args) {
int intValue=100;
long longValue=intValue;
double doubleValue=1234567890;
float floatValue=(float)doubleValue;
System.out.println(floatValue);//1.23456794E9
int X=100;
int Y=200;
System.out.println("X+Y="+X+Y);
System.out.println(X+Y+"=X+Y");
doNotRunme();
String string="";
double d1=1000.123;
double d2=1000.123;
if(Math.abs(d2-d1)<1e-10){
}
//System.out.println(string);
}
public static void doNotRunme()
{
doNotRunme();
}
}
运行截图：
TestBigDecimal.java
源代码：
import java.math.BigDecimal;
public class TestBigDecimal
{
public static void main(String[] args)
{
BigDecimal f1 = new BigDecimal("0.05");
BigDecimal f2 = BigDecimal.valueOf(0.01);
BigDecimal f3 = new BigDecimal(0.05);
System.out.println("下面使用String作为BigDecimal构造器参数的计算结果：");
System.out.println("0.05 + 0.01 = " + f1.add(f2));
System.out.println("0.05 - 0.01 = " + f1.subtract(f2));
System.out.println("0.05 * 0.01 = " + f1.multiply(f2));
System.out.println("0.05 / 0.01 = " + f1.divide(f2));
System.out.println("下面使用double作为BigDecimal构造器参数的计算结果：");
System.out.println("0.05 + 0.01 = " + f3.add(f2));
System.out.println("0.05 - 0.01 = " + f3.subtract(f2));
System.out.println("0.05 * 0.01 = " + f3.multiply(f2));
System.out.println("0.05 / 0.01 = " + f3.divide(f2));
}
}
运行结果：对比两种方法得出误差大小