此题的Employee类设计有缺陷，缺少员工薪水的属性。根据题意只能写出下面的程序：
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abstract class Employee {
public abstract double earnings();
}
class YearWorker extends Employee {
@Override
public double earnings() {
return 0;
}
}
class MonthWorker extends Employee {
@Override
public double earnings() {
return 0;
}
}
class WeekWorker extends Employee {
@Override
public double earnings() {
return 0;
}
}
class Company {
Employee[] employee;
double salaries = 0;
Company(Employee[] employee) {
this.employee = employee;
}
public double salariesPay() {
salaries = 0;
//计算salaries
for(int i=0; iemployee.length; i++) {
salaries += employee[i].earnings();
}
return salaries;
}
}
public class HardWork {
public static void main(String[] args) {
Employee[] employee = new Employee[20];
for(int i=0; iemployee.length; i++) {
if(i % 3 == 0) {
employee[i] = new YearWorker();
}
else if(i % 3 == 1) {
employee[i] = new MonthWorker();
}
else if(i % 3 == 2) {
employee[i] = new WeekWorker();
}
}
Company company = new Company(employee);
System.out.println("公司年工资总额:" + company.salariesPay());
}
}
运行结果：
公司年工资总额:0.0
给你个做好了的Java的源程序的记事本，自己看看就行了的，不怎么难的···
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
public class MyNotepad implements ActionListener{
private JFrame frame=new JFrame("新记事本");
private JTextArea jta=new JTextArea();
private String result="";
private boolean flag=true;
private File f;
private JButton jb=new JButton("开始");
private JTextField jtf=new JTextField(15);
private JTextField jt=new JTextField(15);
private JButton jbt=new JButton("替换为");
private JButton jba=new JButton("全部替换");
private Icon ic=new ImageIcon("D:\\java课堂笔记\\GUI\\11.gif");
private String value;
private int start=0;
private JFrame jf=new JFrame("查找");
private JFrame jfc=new JFrame("替换");
@Override
public void actionPerformed(ActionEvent e) {
String comm=e.getActionCommand();
if("新建".equals(comm)){
if(!(frame.getTitle().equals("新记事本"))){
if(!flag){
write();
newNew();
}else{
JFileChooser jfc=new JFileChooser("D:\\java课堂笔记");
int returnVal = jfc.showDialog(null,"保存为");
if(returnVal == JFileChooser.APPROVE_OPTION) {//选择文件后再执行下面的语句，保证了程序的健壮性
f=jfc.getSelectedFile();
flag=false;
write();
}
}
}else if(!(jta.getText().isEmpty())){
JFileChooser jfc=new JFileChooser("D:\\java课堂笔记");
int returnVal = jfc.showDialog(null,"保存为");
if(returnVal == JFileChooser.APPROVE_OPTION) {//选择文件后再执行下面的语句，保证了程序的健壮性
f=jfc.getSelectedFile();
flag=false;
write();
newNew();
}
}else{
newNew();
}
}else if("打开".equals(comm)){
JFileChooser jfc=new JFileChooser("D:\\java课堂笔记");
jfc.setDialogType(JFileChooser.OPEN_DIALOG);
int returnVal = jfc.showOpenDialog(null);
if(returnVal == JFileChooser.APPROVE_OPTION) {//选择文件后再执行下面的语句，保证了程序的健壮性
f=jfc.getSelectedFile();
frame.setTitle(f.getName());
result=read();
flag=false;
value=result;
jta.setText(result);
}
}else if("保存".equals(comm)){
JFileChooser jfc=new JFileChooser("D:\\java课堂笔记");
if(flag){
int returnVal = jfc.showDialog(null,"保存为");
if(returnVal == JFileChooser.APPROVE_OPTION) {//选择文件后再执行下面的语句，保证了程序的健壮性
f=jfc.getSelectedFile();
flag=false;
write();
}
}else{
write();
}
}else if("另存".equals(comm)){
JFileChooser jfc=new JFileChooser("D:\\java课堂笔记");
int returnVal = jfc.showDialog(null,"另存");
if(returnVal == JFileChooser.APPROVE_OPTION) {//选择文件后再执行下面的语句，保证了程序的健壮性
f=jfc.getSelectedFile();
write();
}
}else if("退出".equals(comm)){
System.exit(0);
}else if("撤销".equals(comm)){
jta.setText(value);
}else if("剪切".equals(comm)){
value=jta.getText();
jta.cut();
}else if("复制".equals(comm)){
jta.copy();
}else if("粘贴".equals(comm)){
value=jta.getText();
jta.paste();
}else if("删除".equals(comm)){
value=jta.getText();
jta.replaceSelection(null);
}else if("全选".equals(comm)){
jta.selectAll();
}else if("查找".equals(comm)){
value=jta.getText();
jf.add(jtf,BorderLayout.CENTER);
jf.add(jb,BorderLayout.SOUTH);
jf.setLocation(300,300);
jf.pack();
jf.setVisible(true);
jf.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
}else if("替换".equals(comm)){
value=jta.getText();
GridLayout gl=new GridLayout(3,3);
JLabel jl1=new JLabel("查找内容:");
JLabel jl2=new JLabel("替换为:");
jfc.setLayout(gl);
jfc.add(jl1);
jfc.add(jtf);
jfc.add(jb);
jfc.add(jl2);
jfc.add(jt);
jfc.add(jbt);
JLabel jl3=new JLabel();
JLabel jl4=new JLabel();
jfc.add(jl3);
jfc.add(jl4);
jfc.add(jba);
jfc.setLocation(300,300);
jfc.pack();
jfc.setVisible(true);
jfc.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
}else if("版本".equals(comm)){
JDialog jd=new JDialog(frame,"关于对话框");
jd.setSize(200,200);
JLabel l=new JLabel("哈哈哈哈哈哈哈哈哈哈呵呵呵呵呵呵呵呵呵呵呵呵呵");
jd.add(l,BorderLayout.CENTER);
jd.setLocation(100,200);
jd.setSize(300,300);
jd.setVisible(true);
// jd.pack();
jd.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
}else if("开始".equals(comm)||"下一个".equals(comm)){
String temp=jtf.getText();
int s=value.indexOf(temp,start);
if(value.indexOf(temp,start)!=-1){
jta.setSelectionStart(s);
jta.setSelectionEnd(s+temp.length());
jta.setSelectedTextColor(Color.GREEN);
start=s+1;
jb.setText("下一个");
// value=value.substring(s+temp.length());//不能截取字串
}else {
JOptionPane.showMessageDialog(jf, "查找完毕!", "提示", 0, ic);
jf.dispose();
}
}else if("替换为".equals(comm)){
String temp=jtf.getText();
int s=value.indexOf(temp,start);
if(value.indexOf(temp,start)!=-1){
jta.setSelectionStart(s);
jta.setSelectionEnd(s+temp.length());
jta.setSelectedTextColor(Color.GREEN);
start=s+1;
jta.replaceSelection(jt.getText());
}else {
JOptionPane.showMessageDialog(jf, "查找完毕!", "提示", 0, ic);
jf.dispose();
}
}else if("全部替换".equals(comm)){
String temp=jta.getText();
temp=temp.replaceAll(jtf.getText(), jt.getText());
jta.setText(temp);
}
}
public String read(){
String temp="";
try {
FileInputStream fis = new FileInputStream(f.getAbsolutePath());
byte[] b=new byte[1024];
while(true){
int num=fis.read(b);
if(num==-1)break;
temp=temp+new String(b,0,num);
}
fis.close();
} catch (Exception e1) {
e1.printStackTrace();
}
return temp;
}
public void write(){
try {
FileOutputStream fos=new FileOutputStream(f);
fos.write(jta.getText().getBytes());
fos.close();
} catch (Exception e) {
e.printStackTrace();
}
}
public void newNew(){
frame.dispose();
new MyNotepad();
flag=true;
}
public MyNotepad(){
JMenuBar jmb=new JMenuBar();
String[] menuLab={"文件","编辑","帮助"};
String[][] menuItemLab={{"新建","打开","保存","另存","退出"},
{"撤销","剪切","复制","粘贴","删除","全选","查找","替换"},
{"版本"}};
for(int i=0;imenuLab.length;i++){
JMenu menu=new JMenu(menuLab[i]);
jmb.add(menu);
for(int j=0;jmenuItemLab[i].length;j++){
JMenuItem jmi=new JMenuItem(menuItemLab[i][j]);
menu.add(jmi);
jmi.addActionListener(this);
}
}
frame.setJMenuBar(jmb);
jta.setLineWrap(true);//自动换行
JScrollPane jsp=new JScrollPane(jta);//滚动窗口面板
frame.add(jsp);
jb.addActionListener(this);
jbt.addActionListener(this);
jba.addActionListener(this);
frame.setLocation(200,50);
frame.setSize(620,660);
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public static void main(String[] args) {
new MyNotepad();
}
}
class Car
{
// 车辆属性
private String brand; // 品牌
private double engineDisplacement;// 排气量
private double speed;// 当前速度
private boolean status;// 启动状态
private double maxSpeed;// 最大速度
public double getSpeed () {
return this.speed;
}
public Car(String brand, double engineDisplacement, double maxSpeed) {
this.brand = brand;
this.engineDisplacement = engineDisplacement;
this.maxSpeed = maxSpeed;
// 其他属性也要有初始值，不然执行出错。
this.speed = 0;
this.status = false;
}
/** 启动 */
public void start() {
this.status = true;
printNowStatus ();
}
/** 关闭（熄火） */
public void stop() {
// 只在速度为0时关闭（貌似楼上两位没仔细看题…）
if (this.speed == 0)
{
this.status = false;
}
printNowStatus ();
}
/** 加速 */
public void speedUp() {
// 只在启动时可以加速
if (this.status)
{
this.speed = this.speed + 20;
if (this.speed this.maxSpeed)
{
this.speed = this.maxSpeed;
}
}
printNowStatus ();
}
/** 减速 */
public void slowDown() {
// 只在启动时可以减速
if (this.status)
{
this.speed = this.speed - 10;
if (this.speed 0)
{
this.speed = 0;
}
}
printNowStatus ();
}
/** 状态打印，在每次启动，加减速，关闭时调用 */
private void printNowStatus () {
System.out.println("轿车【" + this.brand + "】现在的启动状态是：" + this.status + "速度是：" + this.speed +"。");
}
}
public class TestCar
{
public static void main(String[] args)
{
Car myCar = new Car ("红旗", 2, 120);
//启动
myCar.start();
// 循环加速到120
while (myCar.getSpeed() 120)
{
myCar.speedUp();
}
//循环减速
while (myCar.getSpeed() 0)
{
myCar.slowDown();
}
//关闭
myCar.stop();
}
}
/* 直接拿文本写的，我用的电脑没装jdk，楼主自己到Java开发环境下调试，应该没什么问题… */
相当于：System.out.println(test.f());
因为b=a=f();此时的f()已经被子类B重写，所以b=a=f()=2。
即使这么写也是2：
A test = new B();
System.out.println(test.a);
同样，相当于：System.out.println(test.f());
这种情况就是多态了！！
class NoLowerLetterException extends Exception {
public NoLowerLetterException(String msg) {
super(msg);
}
}
class NoDigitException extends Exception {
public NoDigitException(String msg) {
super(msg);
}
}
class People {
void printLetter(char c) {
if (c = 'a' c = 'z') {
System.out.println(c);
} else {
try {
throw new NoLowerLetterException(String.valueOf(c));
} catch (NoLowerLetterException e) {
e.printStackTrace();
}
}
}
void printDigit(char c) {
if (c = '0' c = '9') {
System.out.println(c);
} else {
try {
throw new NoDigitException(String.valueOf(c));
} catch (NoDigitException e) {
e.printStackTrace();
}
}
}
}
public class ExceptionExample {
public static void main(String args[]) {
People people = new People();
for (int i = 0; i 128; i++) {
// 【代码5】
// //将i转换为char类型，执行people.printLetter()方法，如果出现异常则捕获，并输出异常的错误信息！
people.printLetter((char) i);
}
for (int i = 0; i 128; i++) {
// 【代码6】 //将i转换为char类型，执行people. printDigit
// ()方法，如果出现异常则捕获，并输出异常的错误信息！
people.printDigit((char) i);
}
}
}
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Painter extends JFrame{
/**
*
*/
private static final long serialVersionUID = 8160427604782702376L;
CanvasPanel canvas = new CanvasPanel();;
public Painter() {
super("Star");
this.add(canvas);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.pack();
this.setResizable(false);
this.setLocationRelativeTo(null);
this.setVisible(true);
}
public static void main(String[] args) {
new Painter();
}
}
class CanvasPanel extends JPanel implements ActionListener{
/**
*
*/
private static final long serialVersionUID = -4642528854538741028L;
private JButton[] btn = new JButton[4];
private String[] btn_name = {"+", "-", "R", "L"};
private int center_x = 200, center_y = 200, radius = 100, degree = 0;
public CanvasPanel() {
this.setPreferredSize(new Dimension(400, 500));
this.setLayout(null);
for(int i = 0; i 4; i++) {
btn[i] = new JButton(btn_name[i]);
btn[i].setBounds(160 + i * 60, 425, 50, 50);
btn[i].addActionListener(this);
this.add(btn[i]);
}
}
@Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
for(int i = 0; i 5; i++) {
g.drawLine( (int) (center_x + radius * Math.sin(Math.toRadians(degree + 72 * i))),
(int) (center_y - radius * Math.cos(Math.toRadians(degree + 72 * i))),
(int) (center_x + radius * Math.sin(Math.toRadians(degree + 72 * i + 144))),
(int) (center_y - radius * Math.cos(Math.toRadians(degree + 72 * i + 144))));
}
}
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
if(e.getActionCommand() == "+") {
if(radius 200)
radius += 2;
repaint();
} else if(e.getActionCommand() == "-") {
if(radius 0)
radius -= 2;
repaint();
} else if(e.getActionCommand() == "R") {
degree = (degree + 2) % 360;
repaint();
} else if(e.getActionCommand() == "L") {
degree = (degree - 2) % 360;
repaint();
}
}
}
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