计算机自考java实践课

2，求50以内的质数问题。

public class Demo2

{

public static void main(String[]args)

{

int i,j

for(i=2i<=50i++)

{

for(j=2j<=i/2j++)

if(j%i==0)break

if(j>i/2)

System.out.println(i+"是质数")

}

}

}

3，排*问题[注意别把for后面加了号]。

import javax.swing.*

public class Demo15

{

public static void main(String[]args)

{

int n,j,k,space

String result=(String)JOptionPane.showInputDialog(null,"请输入一个整数","输入对话框",JOptionPane.PLAIN_MESSAGE,null,null,null)

n=Integer.parseInt(result)

space=40

for(j=0j<=nj++,space-=2)

{

for(int i=0i<spacei++)

System.out.print(" ")

for(k=1k<=2*j+1k++)

System.out.print(" *")

System.out.print("\n")

}

space+=4

for(j=n-1j>=0j--,space+=2)

{

for(int i=0i<spacei++)

System.out.print(" ")

for(k=1k<=2*j+1k++)

System.out.print(" *")

System.out.print("\n")

}

}

}

5，红绿按钮题：

import javax.swing.*

import java.awt.*

import java.awt.event.*

public class Demo

{

public static void main(String[]args)

{

ButtonDemo myButtonGUI=new ButtonDemo()

myButtonGUI.setVisible(true)

}

}

class ButtonDemo extends JFrame implements ActionListener

{

public static final int Width=200

public static final int Height=250

ButtonDemo()

{

setSize(Width,Height)

setTitle("按钮事件样例")

Container conPane=getContentPane()

conPane.setBackground(Color.YELLOW)

conPane.setLayout(new FlowLayout())

JButton redBut=new JButton("Red")

redBut.addActionListener(this)

conPane.add(redBut)

JButton greenBut=new JButton("Green")

greenBut.addActionListener(this)

conPane.add(greenBut)

}

public void acionPerformed(ActionEvent e)

{

Container conPane=getContentPane()

if(e.getActionCommand().equals("Red"))

conPane.setBackground(Color.RED)

else if(e.getActionCommand().equals("Green"))

conPane.setBackground(Color.GREEN)

else {}

}

}

7，按钮激活文本，显示文本[注意方法是小写，类是大写，所有字母都不能错]

import java.applet.*

import java.awt.*

import java.awt.event.*

public class Demo7 extends Applet implements KeyListener

{

//setSize(400,500)

int count=0

Button button=new Button()

TextArea text=new TextArea(5,20)

public void init()

{

button.addKeyListener(this)

add(button)

add(text)

}

public void keyPressed(KeyEvent e)

{

int t=e.getKeyCode()

if(t>=KeyEvent.VK_A&&t<=KeyEvent.VK_Z)

{

text.append((char)t+" ")count++

if(count%10==0) text.append("\n")

}

}

public void keyTyped(KeyEvent e){}

public void keyReleased(KeyEvent e){}

}

8，单击按钮显示单击的次数，

import javax.swing.*

import java.awt.event.*

import java.applet.*

public class Demo8 extends Applet implements ActionListener

{

int n=0

JButton button=new JButton("单击按钮可以显示点击的次数")

public void init()

{

setSize(800,600)

button.addActionListener(this)

button.setSize(34,3)

add(button)

}

public void actionPerformed(ActionEvent e)

{

n++

button.setText(n+" ")

}

}

9，画五角星。

import java.awt.*

import javax.swing.*

class MyPanel extends JPanel

{

public void paintComponent(Graphics g)

{

int r=100

int x1=100

int x2=(int)(r*(1-Math.cos((18*Math.PI)/180)))

int x3=(int)(r*(1+Math.cos((18*Math.PI)/180)))

int x4=(int)(r*(1-Math.cos((54*Math.PI)/180)))

int x5=(int)(r*(1+Math.cos((54*Math.PI)/180)))

int y1=0

int y2=(int)(r*(1-Math.sin((18*Math.PI)/180)))

int y3=(int)(r*(1-Math.sin((18*Math.PI)/180)))

int y4=(int)(r*(1+Math.sin((54*Math.PI)/180)))

int y5=(int)(r*(1+Math.sin((54*Math.PI)/180)))

g.setColor(Color.RED)

g.drawOval(0,0,200,200)

g.drawLine(x1,y1,x4,y4)

g.drawLine(x1,y1,x5,y5)

g.drawLine(x2,y2,x3,y3)

g.drawLine(x2,y2,x5,y5)

g.drawLine(x3,y3,x4,y4)

}

}

public class Demo9 extends JFrame

{

Demo9()

{

super("Demo9")

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)

getContentPane().add(new MyPanel())

setSize(800,600)

setVisible(true)

}

public static void main(String[]args)

{

new Demo9()

}

}

按照你的要求编写的红绿灯程序，你看看吧，比较简单。

完整的程序如下：

import java.awt.*

import java.awt.event.*

import javax.swing.*

import java.awt.Graphics

public class TrafficLight extends JFrame{

JRadioButton jrbYellow,jrbGreen,jrbRed

int flag=0

jpNewPanel jpNewPanel

public static void main(String[] args){

TrafficLight frame=new TrafficLight()

frame.setSize(500,200)

frame.setLocationRelativeTo(null)

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE)

frame.setTitle("TrafficLight")

frame.setVisible(true)

}

public TrafficLight(){

jpNewPanel=new jpNewPanel()

add(jpNewPanel,BorderLayout.CENTER)

JPanel jpRadioButtons=new JPanel()

jpRadioButtons.setLayout(new GridLayout(1,3))

jpRadioButtons.add(jrbYellow=new JRadioButton("Yellow"))

jpRadioButtons.add(jrbGreen=new JRadioButton("Green"))

jpRadioButtons.add(jrbRed=new JRadioButton("Red"))

add(jpRadioButtons,BorderLayout.SOUTH)

ButtonGroup group=new ButtonGroup()

group.add(jrbYellow)

group.add(jrbGreen)

group.add(jrbRed)

jrbYellow.addActionListener(new ActionListener(){

public void actionPerformed(ActionEvent e){

flag=2

jpNewPanel.repaint()

}

})

jrbGreen.addActionListener(new ActionListener(){

public void actionPerformed(ActionEvent e){

flag=1

jpNewPanel.repaint()

}

})

jrbRed.addActionListener(new ActionListener(){

public void actionPerformed(ActionEvent e){

flag=3

jpNewPanel.repaint()

}

})

}

class jpNewPanel extends JPanel{

protected void paintComponent(Graphics g){

super.paintComponent(g)

g.drawRect(0,0,40,100)

g.drawOval(10,10,20,20)

g.drawOval(10,40,20,20)

g.drawOval(10,70,20,20)

if(flag==1){

g.setColor(Color.GREEN)

g.fillOval(10, 70, 20, 20)

}

else if(flag==2){

g.setColor(Color.YELLOW)

g.fillOval(10, 40, 20, 20)

}

else if(flag==3){

g.setColor(Color.RED)

g.fillOval(10, 10, 20, 20)

}

}

}

}

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