课上动手动脑
Addition.java
兩數相加
源代碼：
// An addition program
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import javax.swing.JOptionPane;? // import class JOptionPane
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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
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????? // read in first number from user as a string
????? firstNumber =
???????? JOptionPane.showInputDialog( "Enter first integer" );
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????? // read in second number from user as a string
????? secondNumber =
???????? JOptionPane.showInputDialog( "Enter second integer" );
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????? // convert numbers from type String to type int
????? number1 = Integer.parseInt( firstNumber );
????? number2 = Integer.parseInt( secondNumber );
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????? // add the numbers
????? sum = number1 + number2;
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????? // display the results
????? JOptionPane.showMessageDialog(
???????? null, "The sum is " + sum, "Results",
???????? JOptionPane.PLAIN_MESSAGE );
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????? System.exit( 0 );?? // terminate the program
?? }
}
感悟：通過彈出對話框的形式先后輸入兩個數并最后計算兩數之和。。
Text Double.Java
源代碼：
package 雙精度;
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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：雙精度直接使用會產生誤差；
EnumTest.java
源代碼：
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public class EnumTest {
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??? public static void main(String[] args) {
??????? Size s=Size.SMALL;
??????? Size t=Size.LARGE;
??????? //s和t引用同一個對象？
??????? System.out.println(s==t);? //
??????? //是原始數據類型嗎？
??????? System.out.println(s.getClass().isPrimitive());
??????? //從字符串中轉換
??????? 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);
??????? }
??? }
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}
?enum Size{SMALL,MEDIUM,LARGE};
感悟：
InputTest.java
/**
?? @version 1.10 2004-02-10
?? @author Cay Horstmann
*/
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import java.util.*;
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public class InputTest
{?
?? public static void main(String[] args)
?? {?
????? Scanner in = new Scanner(System.in);
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????? // get first input
????? System.out.print("What is your name? ");
????? String name = in.nextLine();
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????? // 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));
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?????
?? }
}
感悟：
通過對話框的彈出先輸入姓名年齡最后輸出明年此人的年齡；
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RandomTest.java
源代碼：
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?
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public class RandomStr
{
?????? public static void main(String[] args)
?????? {
????????????? //定義一個空字符串
????????????? String result = "";
????????????? //進行6次循環
????????????? for(int i = 0 ; i < 6 ; i ++)
????????????? {
???????????????????? //生成一個97～122的int型的整數
???????????????????? int intVal = (int)(Math.random() * 26 + 97);
???????????????????? //將intValue強制轉換為char后連接到result后面
???????????????????? result = result + (char)intVal;
????????????? }
????????????? //輸出隨機字符串
????????????? System.out.println(result);
????? }
}
感悟：通過循環產生隨機數，強制轉化類型產生隨機的六位小寫字母；
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SwitchTest.java
源代碼：
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// Drawing shapes
import java.awt.Graphics;
import javax.swing.*;
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public class SwitchTest extends JApplet {
?? int choice;??
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?? public void init()
?? {
????? String input;
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????? input = JOptionPane.showInputDialog(
???????????????? "Enter 1 to draw lines\n" +
???????????????? "Enter 2 to draw rectangles\n" +
???????????????? "Enter 3 to draw ovals\n" );
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????? choice = Integer.parseInt( input );
?? }
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?? 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
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/**************************************************************************
?* (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.???????????????????? *
?*************************************************************************/
運行截圖：
Test.java
源代碼：
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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);
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}
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public static void doNotRunme()
{
?????? doNotRunme();
}
}
運行截圖：
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TestBigDecimal.java
源代碼：
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import java.math.BigDecimal;
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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作為BigDecimal構造器參數的計算結果：");
????????????? 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作為BigDecimal構造器參數的計算結果：");
????????????? 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));
?????? }
}
運行結果：對比兩種方法得出誤差大小
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轉載于:https://www.cnblogs.com/jinseliunian/p/9752396.html
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