求JAVA入门小程序源代码

mport java.util.*;
public class HuiWen
{
public static void main(String[] args)
{
Scanner in=new Scanner(System.in);
System.out.println("please input a String:");
String st=in.nextLine();
String s=st.toLowerCase();
int i=0;
int j=s.length()-1;
boolean t=true;
char first=s.charAt(i);
char last=s.charAt(j);
for(;i {
while(!(first>='a'&&first<='z'))
{
i++;
first=s.charAt(i);
}
while(!(last>='a'&&last<='z'))
{
j--;
last=s.charAt(i);
}
if(i>=j)
break;
if(first==last)
{
i++;
j--;
first=s.charAt(i);
last=s.charAt(j);
}
else
{
t=false;
break;
}
}
if(t)
System.out.println(st+"是回文串");
else
System.out.println(st+"不是回文串");

}
}

//判断是否为回文字串
//什么实用的程序，说具体点！你要计算器的程序吗？
//下面是计算器的程序，把分拿来吧！
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Calculator
{
public static void main(String[] args)
{
CalculatorFrame frame=new CalculatorFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}

class CalculatorFrame extends JFrame
{
public CalculatorFrame()
{
setTitle("Calculator");
CalculatorPanel panel=new CalculatorPanel();
add(panel);
pack();
}
}

class CalculatorPanel extends Panel
{
public CalculatorPanel()
{
setLayout(new BorderLayout());

result=0;
lastCommand="=";
start=true;
flag=true;

display=new JButton("0");
display.setEnabled(false);
add(display,BorderLayout.NORTH);

ActionListener insert=new InsertAction();
ActionListener command=new CommandAction();

panel=new JPanel();
panel.setLayout(new GridLayout(4,5));

addButton("7",insert);
addButton("8",insert);
addButton("9",insert);
addButton("/",command);
addButton("CE",command);

addButton("4",insert);
addButton("5",insert);
addButton("6",insert);
addButton("*",command);
addButton("Backspace",command);

addButton("1",insert);
addButton("2",insert);
addButton("3",insert);
addButton("-",command);
addButton("sqrt",command);

addButton("0",insert);
addButton(".",insert);
addButton("=",command);
addButton("+",command);
addButton("1/x",command);

add(panel,BorderLayout.CENTER);
}
private void addButton(String label,ActionListener listener)
{
JButton button=new JButton(label);
button.addActionListener(listener);
panel.add(button);
}
private class InsertAction implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
String input=event.getActionCommand();
if(start&&flag)
{
display.setText("");
start=false;
}
if(flag)
display.setText(display.getText()+input);
}
}
private class CommandAction implements ActionListener
{
public void actionPerformed(ActionEvent event)
{
String command=event.getActionCommand();

if(command.equals("CE"))
{
display.setText("0");
start=true;
flag=true;
command="=";
}
else
if(start&&flag)
{
if(command.equals("-"))
{
display.setText(command);
start=false;
}
else
if((command.equals("1/x")||command.equals("sqrt"))&&flag)
calculate(Double.parseDouble(display.getText()),command);
else
if(flag)
lastCommand=command;
}
else
{
if(command.equals("Backspace")&&flag)
{
String s=display.getText();
char[] s1=s.toCharArray();
if(s.length()>=2)
{
String s2=new String(s1,0,s.length()-1);
display.setText(s2);
}
else
{
display.setText("0");
start=true;
}

}
else if(flag)
{
calculate(Double.parseDouble(display.getText()),command);

lastCommand=command;
start=true;
}
}
}
}

public void calculate(double x,String command)
{
if(lastCommand.equals("+")) result+=x;
else if(lastCommand.equals("-")) result-=x;
else if(lastCommand.equals("/"))
{
if(x!=0)
result/=x;
else
{
display.setText("除数不能为0");
start=false;
flag=false;
return;
}
}
else if(lastCommand.equals("*")) result*=x;
else if(command.equals("1/x"))
{
if(x!=0)
result=1/x;
else
{
display.setText("除数不能为0");
start=false;
flag=false;
return;
}

}
else if(command.equals("sqrt"))
{
if(x>=0)
result=Math.sqrt(x);
else
{
display.setText("函数输入无效");
start=false;
flag=false;
return;
}
}
else if(lastCommand.equals("=")) result=x;

display.setText(""+result);
}
private JButton display;
private JPanel panel;
private double result;
private String lastCommand;
private boolean start;
private boolean flag;
}

pip7[ip[8;jhj[dryu][pe[]6nu.u.n56[g;h[5

public class HelloWorld{

public static void main(String[] args){

System.out.println("Hello World!")

}

}