helloworld：
class Javahelloworld {
public static void main(String args[]){
System.out.println("hello world\n");
}
}
基本输入输出：
import java.util.Scanner;
public class ScannerTest {
public static void main(String[] args){
Scanner scanner=new Scanner(System.in);
System.out.print("请输入一个数");
int a=scanner.nextInt();
System.out.printf("%d的平方是%d\n",a,a*a);
}
}
Java图形化界面求数的平方：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;/**包含JFrame*/
public class AppGraphInOut {
public static void main(String args[]){
new AppFrame();
}
}
class AppFrame extends JFrame
{
JTextField in=new JTextField(10);
JButton btn=new JButton("求平方");
JLabel out=new JLabel("用于显示平方结果的标签");
public AppFrame()
{
setLayout(new FlowLayout());
getContentPane().add(in);
getContentPane().add(btn);
getContentPane().add(out);
btn.addActionListener(new BtnActionAdapter());
setSize(400,100);
setDefaultCloseOperation(DISPOSE_ON_CLOSE);
setVisible(true);
}
class BtnActionAdapter implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
String s=in.getText();
double d=Double.parseDouble(s);
double sq=d*d;
out.setText(d+"的平方是："+sq);
}
}
}
Java位运算：
public class BitwiseOperators {
public static void main(String args[]){
int a=0b1100;
int b=0b1010;
print("a ",a);
print("b ",b);
print("a&b ",a&b);
print("a|b ",a|b);
print("a^b ",a^b);
print("~a ",~a);
print("a<<2 ",a<<2);
print("a>>2 ",a>>2);
print("a>>>2 ",a>>>2);
}
static void print(String prefix,int n){
String s=Integer.toBinaryString(n);
while(s.length()<4)s="0"+s;
System.out.print(prefix+" "+s+"\n");
}
}
同心圆：
import java.awt.*;
import javax.swing.*;
public class Circle99Frame extends JFrame {
public static void main(String args[])
{
JFrame frame=new Circle99Frame();
frame.setDefaultCloseOperation(DISPOSE_ON_CLOSE);
frame.setSize(600,600);
frame.setVisible(true);
}
public void paint( Graphics g)
{
g.drawString("circle 99",20,20);
int x0=getSize().width/2;
int y0=getSize().height/2;
for(int r=0;r<getSize().height/2;r+=10)
{
g.setColor(getRandomColor());
g.drawOval(x0-r,y0-r,r*2,r*2);
}
}
Color getRandomColor()
{
return new Color(
(int)(Math.random()*255),//random本身只产生（0~1）之间的小数，
(int)(Math.random()*255),
(int)(Math.random()*255)
);
}
}
下面呢是一个常见的简陋的登陆界面，这个程序是这个两个类class共同组成的程序，先看代码：
import javax.swing.JFrame;
import javax.swing.JPanel;
public class DemoFrame extends JFrame{
public DemoFrame(DemoPanel panel)
{
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setSize(300, 200);
this.setTitle("Frame Demo");
this.add(panel);
this.setResizable(false);
this.setVisible(true);
}
public static void main(String[] args)
{
DemoPanel panel = new DemoPanel();
DemoFrame Frame = new DemoFrame(panel);
}
}
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;
public class DemoPanel extends JPanel{
private JLabel labelUser, labelPassWd; //标签 用户名，密码
private JButton buttonLogin, buttonReset; //按钮 登录，重置
private JTextField textFieldUserName; //文本框 用户名输入
private JPasswordField passWdField; //密码框 密码输入
private JPanel panelUserName;
private JPanel panelPassWd;
private JPanel panelLoginButton;
public DemoPanel(){
this.labelUser = new JLabel("用户名");
this.labelPassWd = new JLabel("密 码");
this.buttonLogin = new JButton("登录");
this.buttonReset = new JButton("重置");
this.textFieldUserName = new JTextField(10);
this.passWdField = new JPasswordField(10);
this.panelPassWd = new JPanel();
this.panelUserName = new JPanel();
this.panelLoginButton = new JPanel();
this.setLayout(new GridLayout(3, 1)); //网格式布局
this.panelUserName.add(this.labelUser);
this.panelUserName.add(this.textFieldUserName);
this.panelPassWd.add(this.labelPassWd);
this.panelPassWd.add(this.passWdField);
this.panelLoginButton.add(buttonLogin);
this.panelLoginButton.add(buttonReset);
this.add(this.panelUserName);
this.add(this.panelPassWd);
this.add(this.panelLoginButton);
}
}
程序结果如下 :
简单的加法器：
package TEST;
import javax.swing.JOptionPane; //导入类
public class TEST
{
public static void main(String args[])
{
String input_pane1,input_pane2;
int n1,n2,sum;
input_pane1 = JOptionPane.showInputDialog("Please input the first number"); //输入框1
input_pane2 = JOptionPane.showInputDialog("Please input the second number"); //输入框2
n1 = Integer.parseInt(input_pane1); //获取输入框中输入数据的整数类型
n2 = Integer.parseInt(input_pane2);//获取输入框中输入数据的整数类型
sum = n1+n2;
JOptionPane.showMessageDialog(null, "The sum is: "+sum,"Adding Device",JOptionPane.PLAIN_MESSAGE);
//第1个参数：null 显示在中央
//第2个参数：要显示的字符
//第3个参数：标题栏信息
//第4个参数：对话框类型
System.exit(0); //终结图形用户界面程序必须的
}
}
