常用十题1、九九乘法表：public class chengfa {public static void main(String[] args) {int i,j;System.out.println("9*9乘法表如下：");for(i=1;i<=9;i++){for(j=1;j<=i;j++){System.out.print(+i+"*"+j+"="+i*j);System.out.print(" " );}System.out.println( );}}}2、成绩判断import java.util.Scanner;public class chengjipanduan {public static void main(String[] args) {int grade;System.out.println(" 输入你的成绩：");Scanner s=new Scanner(System.in);grade=s.nextInt();switch(grade/10){case 10:case 9:System.out.println(" 你的成绩为优");break;case 8:System.out.println(" 你的成绩为良");break;case 7:System.out.println(" 你的成绩为中");break;case 6:System.out.println(" 你的成绩为及格");break;case 5:case 4:case 3:case 2:case 1:case 0:System.out.println(" 你的成绩为差");break;}}}3、矩形类public class Rectangle {double width=1.0;double height=1.0;public Rectangle(double width,double height){this.width=width;this.height=height;}public void setwidth(double width){this.width=width;}public double getwidth(double widtht){return width;}public void setheight(double height){this.height=height;}public double getheight(double height){return height;}public double getArea(){return width*height;}public double getperimeter(){return 2*(width+height);}}import tixing06.Rectangle;public class TestRectangle {public static void main(String[] args){Rectangle r=new Rectangle(4,40);System.out.println(" 矩形面积为 "+r.getArea()+" 周长为 "+r.getperimeter());}}4、两数对换package tixing;import java.util.Scanner;public class TiXing02 {public static void main(String[] args) {int a,b;System.out.println(" 输入两个数 a 和 b:");Scanner s=new Scanner(System.in);a=s.nextInt();Scanner k=new Scanner(System.in);b=k.nextInt();System.out.println(" 两个数为 :a="+a+" b="+b);exchange(a,b);}public static void exchange(int a,int b){int t;t=a;a=b;b=t;System.out.println(" 交换后两个数为:a="+a +" b="+b);}}5、数组import java.util.Scanner;import java.util.Random;public class shuzu {public static void main(String[] args) {int n,i,j,k;double ave=0;System.out.println(" 输入数组长度：");Scanner s=new Scanner(System.in);n=s.nextInt();int a[]=new int[n];System.out.println(" 输入的原数组为：");for(i=0;i<n;i++){a[i]=(int)(Math.random()*10+1);System.out.printf("%4d",a[i]);}for(i=0;i<n;i++) {for(j=i+1;j<n;j++){if(a[j]>a[i]){k=a[i];a[i]=a[j];a[j]=k;}}}System.out.println();System.out.println("输入的数组排序为："); for(i=0;i<n;i++){System.out.printf("%4d",a[i]);}int max,min;max=a[0];min=a[0];for(i=0;i<n;i++){if(a[i]>max){max=a[i];}if(a[i]<min){min=a[i];}ave+=a[i];}System.out.println();System.out.println(" System.out.println(" System.out.println("数组中最大数为：数组中最小数为：数组中平均数为："+max);"+min);"+ave/n);}}6、填充圆package tianchongyuan;import java.applet.*;import java.awt.*;public class TianChongY uan extends Applet{ public void paint(Graphics g){g.drawOval(0,0,100,100);g.drawRoundRect(110,10,90,60,50,30);g.setColor(Color.blue);g.fillArc(0,0,100,100,0,360);g.setColor(Color.red);g.fillArc(110,10,90,60,0,360);}7、星形三角形package sanjiaoxing;import java.util.Scanner;public class SanJiaoXing {public static void main(String[] args) {int i,j,n;System.out.println(" 输入层数n:");Scanner s=new Scanner(System.in);n=s.nextInt();for(i=1;i<=n;i++){for(j=0;j<n-i;j++){System.out.printf(" ");}if(i%2!=0){for(j=0;j<2*i-1;j++){System.out.printf("*");}System.out.println("");}else{System.out.printf("*");for(j=0;j<2*i-3;j++){System.out.printf(" ");}System.out.printf("*");System.out.println("");}}}8、一元二次import java.util.Scanner;public class yiyuanerci {public static void main(String[] args) {double a,b,c,m;double x1,x2;System.out.println(" 输入一元二次方程前的三个系数a,b,c:");Scanner s=new Scanner(System.in);a=s.nextDouble();Scanner sc=new Scanner(System.in);b=sc.nextDouble();Scanner sr=new Scanner(System.in);c=sr.nextDouble();m=b*b-4*a*c;if(m>0){System.out.println("两根为x1="+(-b+Math.sqrt(m))/(2*a)+"x2="+(-b-Math.sqrt(m))/(2*a));}elseif(m==0){System.out.println(" 方程有同根为:x1=x2="+(-b/(2*a)));}if(m<0){System.out.println(" 方程无根 ");}}}9、平方根import java.util.Scanner;public class pingfanggeng {public static void main(String[] args) {int a,b,c,m;double x1,x2;Scanner sc=new Scanner(System.in);System.out.println(" 请输入一元二次方程的二次项系数：a=sc.nextInt();Scanner sr=new Scanner(System.in);System.out.println(" 请输入一元二次方程的一次项系数：b=sr.nextInt();Scanner st=new Scanner(System.in);System.out.println(" 请输入一元二次方程的常数项系数："); "); ");c=st.nextInt();m=b*b-4*a*c;x1=(-b+Math.sqrt(m))/(2*a);x2=(-b-Math.sqrt(m))/(2*a);System.out.println(" 一元二次方程的根为： "+x1+""+x2);}}10、简单计算机窗口（此题为JFrame 窗体）import javax.swing.JOptionPane;public class NewJFrame extends javax.swing.JFrame {public NewJFrame() {initComponents();}private void initComponents() {jLabel1 = new javax.swing.JLabel();jLabel2 = new javax.swing.JLabel();jTextField1 = new javax.swing.JTextField();jTextField2 = new javax.swing.JTextField();jButton1 = new javax.swing.JButton();jButton2 = new javax.swing.JButton();setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE); jLabel1.setText(" 第一个数 ");jLabel2.setText(" 第二个数 ");jTextField1.addActionListener(new java.awt.event.ActionListener(){ public void actionPerformed(java.awt.event.ActionEvent evt){jTextField1ActionPerformed(evt);}});jTextField2.addActionListener(new java.awt.event.ActionListener(){ public void actionPerformed(java.awt.event.ActionEvent evt){jTextField2ActionPerformed(evt);}});jButton1.setText(" 计算 ");jButton1.addActionListener(new java.awt.event.ActionListener(){ public void actionPerformed(java.awt.event.ActionEvent evt){jButton1ActionPerformed(evt);}});jButton2.setText(" 取消 ");jButton2.addActionListener(new java.awt.event.ActionListener(){ public void actionPerformed(java.awt.event.ActionEvent evt){jButton2ActionPerformed(evt);}});javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());getContentPane().setLayout(layout);layout.setHorizontalGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING).addGroup(layout.createSequentialGroup().addGap(49, 49, 49).addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignm ent.LEADING).addGroup(layout.createSequentialGroup().addGroup(layout.createParallelGroup(javax.swing.GroupLayou t.Alignment.LEADING).addComponent(jLabel2).addComponent(jLabel1)).addGap(82, 82, 82).addGroup(layout.createParallelGroup(javax.swing.GroupLayou t.Alignment.LEADING, false).addComponent(jTextField1,javax.swing.GroupLayout.PREFERRED_SIZE, 75,javax.swing.GroupLayout.PREFERRED_SIZE).addComponent(jTextField2,javax.swing.GroupLayout.PREFERRED_SIZE, 75,javax.swing.GroupLayout.PREFERRED_SIZE))).addGroup(layout.createSequentialGroup().addComponent(jButton1).addGap(125, 125, 125).addComponent(jButton2))).addContainerGap(112, Short.MAX_V ALUE)));layout.setVerticalGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING).addGroup(layout.createSequentialGroup().addGap(31, 31, 31).addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignm ent.BASELINE).addComponent(jLabel1).addComponent(jTextField1,javax.swing.GroupLayout.PREFERRED_SIZE,javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)).addGap(35, 35, 35).addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignm ent.BASELINE).addComponent(jLabel2).addComponent(jTextField2,javax.swing.GroupLayout.PREFERRED_SIZE,javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)).addGap(40, 40, 40).addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignm ent.BASELINE).addComponent(jButton1).addComponent(jButton2)).addContainerGap(129, Short.MAX_V ALUE)));pack();}private void jTextField1ActionPerformed(java.awt.event.ActionEvent evt) {}private void jTextField2ActionPerformed(java.awt.event.ActionEvent evt) {}private void jButton1ActionPerformed(java.awt.event.ActionEvent evt){ double qiuhe;qiuhe = Double.parseDouble(jTextField1.getText()) +Double.parseDouble(jTextField2.getText());JOptionPane.showMessageDialog(null,qiuhe);}private void jButton2ActionPerformed(java.awt.event.ActionEvent evt){ dispose();System.exit(0);// TODO add your handling code here:}public static void main(String args[]) {/* Set the Nimbus look and feel *///<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">/* If Nimbus (introduced in Java SE 6) is not available, stay with the default lookand feel.* For details see/javase/tutorial/uiswing/lookandfeel/plaf.html*/try {for(javax.swing.UIManager.LookAndFeelInfo info: javax.swing.UIManager.getInstalledLookAndFeels()) {if ("Nimbus".equals(info.getName())) {javax.swing.UIManager.setLookAndFeel(info.getClassName());break;}}} catch (ClassNotFoundException ex) {java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level. SEVERE, null, ex);} catch (InstantiationException ex) {java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level. SEVERE, null, ex);} catch (IllegalAccessException ex) {java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level. SEVERE, null, ex);} catch (javax.swing.UnsupportedLookAndFeelException ex) {java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level. SEVERE, null, ex);}//</editor-fold>/* Create and display the form */java.awt.EventQueue.invokeLater(new Runnable() {public void run() {new NewJFrame().setVisible(true);}});}// Variables declaration - do not modifyprivate javax.swing.JButton jButton1;private javax.swing.JButton jButton2;private javax.swing.JLabel jLabel1;private javax.swing.JLabel jLabel2;private javax.swing.JTextField jTextField1;private javax.swing.JTextField jTextField2;// End of variables declaration}。