数组的使用

package javaDemo;

import java.util.*;

/**

*

* @author Administrator

* @version 1.0

*

*

*/

public class test {

public static void main(String[] args)

{

String[] greeting = new String[3];

greeting[0] = "Welcome to Core Java";

greeting[1] = "by Cay Horstmann";

greeting[2] = "and Gary Cornell";

for (String g : greeting)

System.out.println(g);

}

}

eclipse格式化快捷键Ctrl+Shift+F

jFrame

package javaDemo;

/**

*

* @author Administrator

* @version 1.0

*

*

*/

import java.awt.*;

import java.awt.event.*;

import java.io.*;

import javax.swing.*;

/**

* A program for viewing images.

*/

public class ImageViewer {

public static void main(String[] args) {

JFrame frame = new ImageViewerFrame();

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setVisible(true);

}

}

/**

* A frame with a label to show an image.

*/

class ImageViewerFrame extends JFrame {

public ImageViewerFrame() {

setTitle("ImageViewer");

setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);

// use a label to display the images

label = new JLabel();

add(label);

// set up the file chooser

chooser = new JFileChooser();

chooser.setCurrentDirectory(new File("."));

// set up the menu bar

JMenuBar menuBar = new JMenuBar();

setJMenuBar(menuBar);

JMenu menu = new JMenu("文件");

menuBar.add(menu);

JMenuItem openItem = new JMenuItem("打开");

menu.add(openItem);

openItem.addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent event) {

// show file chooser dialog

int result = chooser.showOpenDialog(null);

// if file selected, set it as icon of the label

if (result == JFileChooser.APPROVE_OPTION) {

String name = chooser.getSelectedFile().getPath();

label.setIcon(new ImageIcon(name));

}

}

});

JMenuItem exitItem = new JMenuItem("退出");

menu.add(exitItem);

exitItem.addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent event) {

System.exit(0);

}

});

}

private JLabel label;

private JFileChooser chooser;

private static final int DEFAULT_WIDTH = 400;

private static final int DEFAULT_HEIGHT = 500;

}

BigIntegerTest

package javaDemo; //首先要引入包

/**

* @version 1.20 2004-02-10

* @author Cay Horstmann

*

**/

import java.math.*; //引入一些math相关的东西

import java.util.*;

public class BigIntegerTest //类名和文件名要相同

{

public static void main(String[] args) //主函数也就是入口函数

{

Scanner in = new Scanner(System.in); //键盘输入的对象

System.out.print("How many numbers do you need to draw? ");

int k = in.nextInt(); //获取数据，存入变量k中

System.out.print("What is the highest number you can draw? ");

int n = in.nextInt(); //获取数据，存入变量n中

/*

compute binomial coefficient

n * (n - 1) * (n - 2) * . . . * (n - k + 1)

-------------------------------------------

1 * 2 * 3 * . . . * k

*/

BigInteger lotteryOdds = BigInteger.valueOf(1);

for (int i = 1; i <= k; i++)

lotteryOdds = lotteryOdds

.multiply(BigInteger.valueOf(n - i + 1))

.divide(BigInteger.valueOf(i));

System.out.println("Your odds are 1 in " + lotteryOdds + ". Good luck!");//进行一些处理

}

}

稍微复杂的算法

package javaDemo; //首先要引入包

/**

@version 1.40 2004-02-10

@author CayHorstmann

*/

public class CompoundInterest

{

public static void main(String[] args)

{

final int STARTRATE = 10; //定义常量

final int NRATES = 6;

final int NYEARS = 10;

// set interest rates to 10 . . . 15%

double[] interestRate = new double[NRATES]; //新建数组

for (int j = 0; j < interestRate.length; j++)

interestRate[j] = (STARTRATE + j) / 100.0; //给数组赋值

double[][] balances = new double[NYEARS][NRATES]; //定义二维数组

// set initial balances to 10000

for (int j = 0; j < balances[0].length; j++)

balances[0][j] = 10000;

// compute interest for future years

for (int i = 1; i < balances.length; i++)

{

for (int j = 0; j < balances[i].length; j++)

{

// get last year's balances from previous row

double oldBalance = balances[i - 1][j];

// compute interest

double interest = oldBalance * interestRate[j];

// compute this year's balances

balances[i][j] = oldBalance + interest;

}

}

// print one row of interest rates

for (int j = 0; j < interestRate.length; j++)

System.out.printf("%9.0f%%", 100 * interestRate[j]);

System.out.println();

// print balance table

for (double[] row : balances)

{

// print table row

for (double b : row)

System.out.printf("%10.2f", b);

System.out.println();

}

}

}

同一个包下可以互相引用类，并使用其中方法

CompoundInterest comp = new CompoundInterest();

comp.main(args);

package javaDemo; //首先要引入包

/**

@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("你叫什么名字? ");

String name = in.nextLine();

// get second input

System.out.print("你多大了? ");

int age = in.nextInt();

// display output on console

System.out.println("你好, " + name + ". 明年, 你的年龄将会是 " + (age + 1));

}

}

如何调整console字体大小？

打开window - preferences-- general - appearance - colors and fonts --debug - console font 就可以调节了。

我表示看不懂，这算法太复杂了，工作这么久，都不懂。

package javaDemo;

/**

@version 1.20 2004-02-10

@author Cay Horstmann

*/

public class LotteryArray

{

public static void main(String[] args)

{

final int NMAX = 5; //定义常量

// allocate triangular array

int[][] odds = new int[NMAX + 1][]; //定义数组

for (int n = 0; n <= NMAX; n++)

odds[n] = new int[n + 1];

// fill triangular array

for (int n = 0; n < odds.length; n++)

for (int k = 0; k < odds[n].length; k++)

{

/*

compute binomial coefficient

n * (n - 1) * (n - 2) * . . . * (n - k + 1)

-------------------------------------------

1 * 2 * 3 * . . . * k

*/

int lotteryOdds = 1;

for (int i = 1; i <= k; i++)

lotteryOdds = lotteryOdds * (n - i + 1) / i;

odds[n][k] = lotteryOdds;

}

// print triangular array

for (int[] row : odds)

{

for (int odd : row)

System.out.printf("%4d", odd);

System.out.println();

}

}

}

表示作者很牛逼。

/**

@version 1.20 2004-02-10

@author Cay Horstmann

*/

package javaDemo;

import java.util.*;

public class LotteryDrawing

{

public static void main(String[] args)

{

Scanner in = new Scanner(System.in);

System.out.print("How many numbers do you need to draw? ");

int k = in.nextInt();

System.out.print("What is the highest number you can draw? ");

int n = in.nextInt();

// fill an array with numbers 1 2 3 . . . n

int[] numbers = new int[n]; //定义一维数组

for (int i = 0; i < numbers.length; i++)

numbers[i] = i + 1;//赋值

// draw k numbers and put them into a second array

int[] result = new int[k];

for (int i = 0; i < result.length; i++)

{

// make a random index between 0 and n - 1

int r = (int) (Math.random() * n); //直接使用Math的random方法

// pick the element at the random location

result[i] = numbers[r];

// move the last element into the random location

numbers[r] = numbers[n - 1];

n--;

}

// print the sorted array

Arrays.sort(result); //排序数组

System.out.println("Bet the following combination. It'll make you rich!");

for (int r : result)

System.out.println(r);

}

}

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