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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