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import java.awt.BorderLayout;import java.awt.Container;import java.awt.Font;import java.awt.GridLayout;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JOptionPane;import javax.swing.JPanel;import javax.swing.JTextField;public class TimerDemo extends JFrame implements ActionListener { private static final long serialVersionUID = 201306211111L; private JTextField screen = new JTextField("0"); private JButton start = new JButton("开始"); private JButton reset = new JButton("重置"); private JPanel panel = new JPanel(); private boolean isRunning; private int time; private int timeBetween; public TimerDemo(int timeBetween) { super("计时器"); this.timeBetween = timeBetween; try { init(); } catch (Exception e) { e.printStackTrace(); } } public TimerDemo() { super("计时器"); this.timeBetween = 100; try { init(); } catch (Exception e) { e.printStackTrace(); } } private void init() { panel.setLayout(new GridLayout()); panel.add(start); panel.add(reset); start.addActionListener(this); reset.addActionListener(this); screen.setFont(new Font("幼圆", Font.BOLD, 60)); screen.setHorizontalAlignment(JTextField.CENTER); screen.setEditable(false); Container c = getContentPane(); c.setLayout(new BorderLayout()); c.add(panel, BorderLayout.SOUTH); c.add(screen, BorderLayout.CENTER); this.setSize(200, 150); this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); this.setResizable(false); this.setLocationRelativeTo(null); this.setVisible(true); } public static void main(String[] args) { new TimerDemo(1);// 设定 1ms/次 // new TimerDemo(); } @Override public void actionPerformed(ActionEvent e) { if (e.getSource() == start) { if (start.getText().equals("开始")) { start.setText("暂停"); isRunning = true; } else if (start.getText().equals("暂停")) { start.setText("开始"); isRunning = false; } } if (e.getSource() == reset) { start.setText("开始"); screen.setText("0"); isRunning = false; time = 0; } new Thread(new TimeZone()).start(); } class TimeZone implements Runnable { @Override public void run() { while (isRunning) { time++; if (time = Integer.MAX_VALUE) { screen.setText("ERROR"); JOptionPane.showMessageDialog(null, "ERROR"); isRunning = false; } screen.setText(String.valueOf(time)); try { Thread.sleep(timeBetween); } catch (Exception e) { e.printStackTrace(); } } } }}
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import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class General extends JFrame implements ActionListener
{
String args[]={"退格","总清","清零","/","1","2","3","+","4","5","6","-","7","8","9","*","0","+/-",".","="};
JButton jb[]=new JButton[20];
JPanel p1=new JPanel();
JTextField jtf=new JTextField(15);
double num1,num2,jieguo;
char c,ch;
public General()
{
Container ct=getContentPane();
jtf.addKeyListener(new KA());
jtf.setHorizontalAlignment(JTextField.RIGHT);
ct.add(jtf,"North");
p1.setLayout(new GridLayout(5,4));
for(int i=0;i20;i++)
{
jb[i]=new JButton(args[i]);
jb[i].addActionListener(this);
p1.add(jb[i]);
}
ct.add(p1);
pack();
setVisible(true);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String args[])
{
new General();
}
public void actionPerformed(ActionEvent e)// 监听按键
{
String str=e.getActionCommand().trim();
if("0123456789.".indexOf(str)!=-1)
{
if(jtf.getText().equals("0"))jtf.setText(null);
jtf.setText(jtf.getText()+str);
return;
}
if("+-*/".indexOf(str)!=-1)
{
num1=Double.parseDouble(jtf.getText());
c=str.charAt(0);
jtf.setText(null);
return;
}
else if(str.equals("="))
{
num2=Double.parseDouble(jtf.getText());
switch(c)
{
case '+': jieguo=num1+num2; break;
case '-': jieguo=num1-num2; break;
case '*': jieguo=num1*num2; break;
case '/': jieguo=num1/num2; break;
}
jtf.setText(Double.toString(jieguo));
}
else if(str.equals("+/-"))
{
if(jtf.getText().isEmpty()==false)
{
Double lnum=-(Double.parseDouble(jtf.getText()));
jtf.setText(Double.toString(lnum));
}
else
{
jtf.setText("-");
}
}
else if(str.equals("清空"))
{
jtf.setText(null);
}
else if(str.equals("清零"))
{
jtf.setText("0");
}
else if(str.equals("退格"))
{
jtf.setText(jtf.getText().substring(0,jtf.getText().length()-1));
}
}
class KA extends KeyAdapter // 监听键盘
{
public void keyPressed(KeyEvent e)
{
char ch=e.getKeyChar();
if("+-*/".indexOf(ch)!=-1)
{
num1=Double.parseDouble(jtf.getText());
c=ch;
}
if(ch=='='|ch==e.VK_ENTER)
{
num2=Double.parseDouble(jtf.getText());
switch(c)
{
case '+': jieguo=num1+num2; break;
case '-': jieguo=num1-num2; break;
case '*': jieguo=num1*num2; break;
case '/': jieguo=num1/num2; break;
}
}
}
public void keyReleased(KeyEvent e)
{
char ch=e.getKeyChar();
if("+-*/".indexOf(ch)!=-1)
{
jtf.setText(null);
}
if(ch=='='|e.getKeyCode()==e.VK_ENTER)
{
jtf.setText(Double.toString(jieguo));
}
}
}
}
代码如下：
public class Test
{
public static void main(String[] args)
{
for(int i =10; i=1 ; i--)
{
System.out.print(i);
System.out.print(" ");
}
}
}
以上代码可灵活的变动for里的i初始值。
//倒数
double y=(double)1/123;//1除以任何数 就是他本身的倒数 这里把1/123强转为double类型
System.out.println("y的倒数为"+y);
int x =123;//x可以为任意数0-x就是x的相反数
System.out.println((0-x));
//绝对值
int a =-15;
int b=Math.abs(a);
System.out.println(b);