《Java语言程序设计》答案

《Java语言程序设计》答案第一套题一、简答题1什么是多态性?方法的重载和覆盖有何区别?阅读下列代码，指出其中存在的重载和覆盖，写出输出结果是什么？解释为什么这样输出?(15分)classC1{ publicvoidf(){ System.out.println("C1.f"); }}classC2extendsC1{ publicvoidf(){ System.out.println("C2.f"); }}classC3{ publicvoidg(C1one){ System.out.println("g(C1)"); one.f(); } publicvoidg(C2two){ System.out.println("g(C2)"); two.f(); }}publicclassMain1{ publicstaticvoidmain(String[]args){ C1one=newC2(); C3three=newC3(); three.g(one); }}答：在Java语言中，多态是指一个方法可以有多种实现版本，类的多态性表现为方法的多态性。方法重载，指的是在类中创建多个具有相同名称，但使用不同参数的方法，Java虚拟机根据传递给方法的参数个数的类型决定调用哪个重载方法。方法的覆盖指在子类中重新定义父类中已有的方法，对于重写的方法，运行时系统根据调用该方法的实例的类型来决定选择哪个方法调用。输出结果为g(C1)C2.f解释：变量three的类型是C3,变量one声明为C1类型。C3的g()方法有两个重载实现，当传入的参数为C1类型时，输出为g(C1)。又因为变量one指向的是C1的子类C2的对象，C2的f方法覆盖了C1的f方法，所以在C3.g()的方法中执行时，执行的是C2.f()，所以输出为C2.f。2、请用自己的语言介绍throw/throws有什么联系和区别？在程序中应如何使用？另外谈谈final、finally的区别和作用，必须举例说明用法。(15分)答：throw是在代码块内的，即在捕获方法内的异常并抛出时用的；throws是针对方法的，即将方法的异常信息抛出去。可以理解为throw是主动（在方法内容里我们是主动捕获并throw的），而throws是被动（在方法上是没有捕获异常进行处理，直接throws的）例子：publicvoidstr2int(Stringstr)throwsException{//这里将得到的异常向外抛出try{System.out.println(Integer.parseInt(str));}catch(NumberFormatExceptione){//TODO这里可以做一些处理，处理完成后将异常报出，让外层可以得到异常信息thrownewException("格式化异常");}}final是用来修饰名词的，即它是用来表达最终的某个东西的。比如，“最后的战役”，“最后的晚餐”，“最后的结局”之类的。finally是用来修饰名词以外的词的（经常是修饰动词用的），即它是用来表达最终的一个行为或动作的。比如“他最后还是来了”“你最后赢了没”“钱最终怎么算的”finalize是动词，它不修饰其他词，它就是表达了一种“了结，完成，完善，搞定”的一个行为。就比如“咱把这事了结了吧”“把题目做完”“把工作做完”三个词都跟“完结”有关，前两个只是表达某件事情已经完结时是什么样的。而第三个词，它的作用在于把一个没完结的东西变到已经完结的状态，是一种行为。3、编写一个描述学生基本情况的类，属性包括姓名，学号，语文成绩，数学成绩和英语成绩，方法包括信息输出，设置姓名和学号，设置三门课程成绩，计算总成绩和平均成绩。在main方法中对方法进行测试(15分)4、Java中实现多线程有几种方式？这几种方式有什么区别？然后采取其中一种方式设计一个线程例子，在例子中构造4个线程对象实现对同一数据类对象进行操作(数据初始值为0)，其中线程对象1对数据执行+10的操作，线程对象2对数据执行+20的操作,对象3对数据执行乘以3的操作，线程对象4对数据执行除以4的操作,，要求考虑线程同步，保证数据操作的正确性。要求提供程序代码以及运行结果截图（15分)有三种方式：通过实现Runnable接口；通过继承Thread类；以及通过Callable和Future创建线程。采用实现Runnable、Callable接口的方式创建多线程时，线程类只是实现了Runnable接口或Callable接口，还可以继承其他类。使用继承Thread类的方式创建多线程时，编写简单，如果需要访问当前线程，则无需使用Thread.currentThread()方法，直接使用this即可获得当前线程。二、编程题1、编写一个图形用户界面程序，包含两个按钮，一个信息标签（label）和一个显示面板，两个按钮分别为“掷色子”和“移动”，在显示面板中显示一个小人（用小圆以及线绘制），随机设定小人的初始位置，当点击“掷色子”按钮，随机产生移动信息（上移，下移，左移，右移，移动几步）,并显示在信息标签中，点击移动，按照产生的移动信息，让小人进行移动。要求提供完整程序代码以及运行结果截图（20分)答：/**Tochangethislicenseheader,chooseLicenseHeadersinProjectProperties.*Tochangethistemplatefile,chooseTools|Templates*andopenthetemplateintheeditor.*/packagetest;importjava.awt.Color;importjava.awt.EventQueue;importjava.awt.Graphics;importjava.awt.Graphics2D;importjava.util.Random;importjavax.swing.JFrame;/****@authorldl*/publicclassTestLableextendsjavax.swing.JFrame{privatejavax.swing.JButtonjButton1;privatejavax.swing.JButtonjButton2;privatejavax.swing.JLabeljLabel1; publicTestLable(){initComponents();}@SuppressWarnings("unchecked")privatevoidinitComponents(){jLabel1=newjavax.swing.JLabel();jButton1=newjavax.swing.JButton();jButton2=newjavax.swing.JButton();setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);jLabel1.setText("开始点击掷");jButton1.setText("掷色子");jButton1.addActionListener(newjava.awt.event.ActionListener(){publicvoidactionPerformed(java.awt.event.ActionEventevt){jButton1ActionPerformed(evt);}});jButton2.setText("移动");jButton2.addActionListener(newjava.awt.event.ActionListener(){publicvoidactionPerformed(java.awt.event.ActionEventevt){jButton2ActionPerformed(evt);}});javax.swing.GroupLayoutlayout=newjavax.swing.GroupLayout(getContentPane());getContentPane().setLayout(layout);layout.setHorizontalGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING).addGroup(layout.createSequentialGroup().addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING).addGroup(layout.createSequentialGroup().addGap(34,34,34).addComponent(jLabel1)).addGroup(layout.createSequentialGroup().addGap(24,24,24).addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING,false).addComponent(jButton1,javax.swing.GroupLayout.DEFAULT_SIZE,javax.swing.GroupLayout.DEFAULT_SIZE,Short.MAX_VALUE).addComponent(jButton2,javax.swing.GroupLayout.DEFAULT_SIZE,javax.swing.GroupLayout.DEFAULT_SIZE,Short.MAX_VALUE)))).addContainerGap(306,Short.MAX_VALUE)));layout.setVerticalGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING).addGroup(layout.createSequentialGroup().addGap(18,18,18).addComponent(jLabel1).addGap(26,26,26).addComponent(jButton1).addGap(18,18,18).addComponent(jButton2).addContainerGap(177,Short.MAX_VALUE)));pack();}intrandomNum=0;intrandomPosition=0;String[]strs={"上移","下移","左移","右移"};privatevoidjButton1ActionPerformed(java.awt.event.ActionEventevt){/Randomrandom=newRandom();randomNum=random.nextInt(4)+1;randomPosition=random.nextInt(4);jLabel1.setText(strs[randomPosition]+randomNum+"步");}privatevoidjButton2ActionPerformed(java.awt.event.ActionEventevt){repaint();}publicstaticvoidmain(Stringargs[]){try{for(javax.swing.UIManager.LookAndFeelInfoinfo:javax.swing.UIManager.getInstalledLookAndFeels()){if("Nimbus".equals(info.getName())){javax.swing.UIManager.setLookAndFeel(info.getClassName());break;}}}catch(ClassNotFoundExceptionex){java.util.logging.Logger.getLogger(TestLable.class.getName()).log(java.util.logging.Level.SEVERE,null,ex);}catch(InstantiationExceptionex){java.util.logging.Logger.getLogger(TestLable.class.getName()).log(java.util.logging.Level.SEVERE,null,ex);}catch(IllegalAccessExceptionex){java.util.logging.Logger.getLogger(TestLable.class.getName()).log(java.util.logging.Level.SEVERE,null,ex);}catch(javax.swing.UnsupportedLookAndFeelExceptionex){java.util.logging.Logger.getLogger(TestLable.class.getName()).log(java.util.logging.Level.SEVERE,null,ex);}/*Createanddisplaytheform*/java.awt.EventQueue.invokeLater(newRunnable(){publicvoidrun(){newTestLable().setVisible(true);}});}@Overridepublicvoidpaint(Graphicsg){super.paint(g);//String[]strs={"上移","下移","左移","右移"};switch(randomPosition){case0:y=y-randomNum*10;y1=y1-randomNum*10;y2=y2-randomNum*10;y11=y11-randomNum*10;y22=y22-randomNum*10;break;case1:y=y+randomNum*10;y1=y1+randomNum*10;y2=y2+randomNum*10;y11=y11+randomNum*10;y22=y22+randomNum*10;break;case2:x=x-randomNum*10;x1=x1-randomNum*10;x11=x11-randomNum*10;x2=x2-randomNum*10;x22=x22-randomNum*10;break;case3:x=x+randomNum*10;x1=x1+randomNum*10;x11=x11+randomNum*10;x2=x2+randomNum*10;x22=x22+randomNum*10;break;default:break;}g.drawOval(x,y,20,20);g.drawLine(x1,y1,x11,y11);g.drawLine(x2,y2,x22,y22);}intx=200;inty=150;intx1=200;inty1=165;intx11=199;inty11=180;intx2=220;inty2=165;intx22=220;inty22=182;}2、编写一个班级推优（优秀学生干部）投票管理程序。列出参与推优的学生名单（6名），可以勾选进行投票，要求每个参选学生前面有图标表示候选人的职务，每人可以投3票，每次投票后能够显示当前投票人数以及每名候选者得票数，图形化柱状图显示得票数，可以保存投票结果到文本文件。要求提供完整程序代码以及运行结果截图(20分)答：/**Tochangethislicenseheader,chooseLicenseHeadersinProjectProperties.*Tochangethistemplatefile,chooseTools|Templates*andopenthetemplateintheeditor.*/packagetest;importjava.awt.BorderLayout;importjava.awt.Font;importjava.util.List;importjavax.swing.JCheckBox;importorg.jfree.chart.ChartFactory;importorg.jfree.chart.ChartPanel;importorg.jfree.chart.JFreeChart;importorg.jfree.chart.axis.CategoryAxis;importorg.jfree.chart.axis.NumberAxis;importorg.jfree.chart.axis.ValueAxis;importorg.jfree.chart.plot.CategoryPlot;importorg.jfree.chart.plot.PlotOrientation;importorg.jfree.data.category.CategoryDataset;importorg.jfree.data.category.DefaultCategoryDataset;/****@authorldl*/publicclassTestClassextendsjavax.swing.JFrame{privateDefaultCategoryDatasetdataset;publicTestClass(){initComponents();CategoryDatasetdataset=getDataSet();JFreeChartchart=ChartFactory.createBarChart("统计",//图表标题"投票统计",//目录轴的显示标签"数量",//数值轴的显示标签dataset,//数据集PlotOrientation.VERTICAL,//图表方向：水平、垂直true,false,false);CategoryPlotplot=chart.getCategoryPlot();//获取图表区域对象NumberAxisnumberaxis=(NumberAxis)plot.getRangeAxis();numberaxis.setStandardTickUnits(NumberAxis.createIntegerTickUnits());CategoryAxisdomainAxis=plot.getDomainAxis();//水平底部列表domainAxis.setLabelFont(newFont("黑体",Font.BOLD,14));//水平底部标题domainAxis.setTickLabelFont(newFont("宋体",Font.BOLD,12));//垂直标题ValueAxisrangeAxis=plot.getRangeAxis();//获取柱状rangeAxis.setLabelFont(newFont("黑体",Font.BOLD,15));chart.getLegend().setItemFont(newFont("黑体",Font.BOLD,15));chart.getTitle().setFont(newFont("宋体",Font.BOLD,20));//设置标题字体ChartPanelchartPanel=newChartPanel(chart,true);jPanel1.setLayout(newBorderLayout(0,0));jPanel1.add(chartPanel);jPanel1.repaint();}/***Thismethodiscalledfromwithintheconstructortoinitializetheform.*WARNING:DoNOTmodifythiscode.Thecontentofthismethodisalways*regeneratedbytheFormEditor.*/@SuppressWarnings("unchecked")//<editor-folddefaultstate="collapsed"desc="GeneratedCode">privatevoidinitComponents(){jCheckBox1=newjavax.swing.JCheckBox();jPanel1=newjavax.swing.JPanel();jCheckBox5=newjavax.swing.JCheckBox();jCheckBox2=newjavax.swing.JCheckBox();jCheckBox3=newjavax.swing.JCheckBox();jCheckBox6=newjavax.swing.JCheckBox();jCheckBox4=newjavax.swing.JCheckBox();jButton1=newjavax.swing.JButton();setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);jCheckBox1.setText("班长张三");jCheckBox1.addActionListener(newjava.awt.event.ActionListener(){publicvoidactionPerformed(java.awt.event.ActionEventevt){jCheckBox1ActionPerformed(evt);}});javax.swing.GroupLayoutjPanel1Layout=newjavax.swing.GroupLayout(jPanel1);jPanel1.setLayout(jPanel1Layout);jPanel1Layout.setHorizontalGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING).addGap(0,411,Short.MAX_VALUE));jPanel1Layout.setVerticalGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING).addGap(0,0,Short.MAX_VALUE));jCheckBox5.setText("学习张三4");jCheckBox5.addActionListener(newjava.awt.event.ActionListener(){publicvoidactionPerformed(java.awt.event.ActionEventevt){jCheckBox5ActionPerformed(evt);}});jCheckBox2.setText("卫生张三1");jCheckBox2.addActionListener(newjava.awt.event.ActionListener(){publicvoidactionPerformed(java.awt.event.ActionEventevt){jCheckBox2ActionPerformed(evt);}});jCheckBox3.setText("学习张三2");jCheckBox3.addActionListener(newjava.awt.event.ActionListener(){publicvoidactionPerformed(java.awt.event.ActionEventevt){jCheckBox3ActionPerformed(evt);}});jCheckBox6.setText("学习张三5");jCheckBox6.addActionListener(newjava.awt.event.ActionListener(){publicvoidactionPerformed(java.awt.event.ActionEventevt){jCheckBox6ActionPerformed(evt);}});jCheckBox4.setText("学习张三3");jCheckBox4.addActionListener(newjava.awt.event.ActionListener(){publicvoidactionPerformed(java.awt.event.ActionEventevt){jCheckBox4ActionPerformed(evt);}});jButton1.setText("投票");javax.swing.GroupLayoutlayout=newjavax.swing.GroupLayout(getContentPane());getContentPane().setLayout(layout);layout.setHorizontalGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING).addGroup(layout.createSequentialGroup().addContainerGap().addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING).addComponent(jCheckBox1).addComponent(jCheckBox2).addComponent(jCheckBox3).addComponent(jCheckBox4).addComponent(jCheckBox5).addComponent(jCheckBox6).addComponent(jButton1)).addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED).addComponent(jPanel1,javax.swing.GroupLayout.DEFAULT_SIZE,javax.swing.GroupLayout.DEFAULT_SIZE,Short.MAX_VALUE)));layout.setVerticalGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING).addGroup(layout.createSequentialGroup().addGap(14,14,14).addComponent(jCheckBox1).addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED).addComponent(jCheckBox2).addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED).addComponent(jCheckBox3).addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED).addComponent(jCheckBox4).addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED).addComponent(jCheckBox5).addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED).addComponent(jCheckBox6).addGap(18,18,18).addComponent(jButton1).addContainerGap(83,Short.MAX_VALUE)).addComponent(jPanel1,javax.swing.GroupLayout.DEFAULT_SIZE,javax.swing.GroupLayout.DEFAULT_SIZE,Short.MAX_VALUE));pack();}//</editor-fold>privatevoidjCheckBox1ActionPerformed(java.awt.event.ActionEventevt){JCheckBoxjCheckBox=(JCheckBox)evt.getSource();intintValue=dataset.getValue(0,0).intValue();if(jCheckBox.isSelected()){intValue++;}else{intValue--;}dataset.setValue(intValue,"张三1","张三1");}privatevoidjCheckBox5ActionPerformed(java.awt.event.ActionEventevt){//TODOaddyourhandlingcodehere:JCheckBoxjCheckBox=(JCheckBox)evt.getSource();intintValue=dataset.getValue(4,4).intValue();if(jCheckBox.isSelected()){intValue++;}else{intValue--;}dataset.setValue(intValue,"张三4","张三4");}privatevoidjCheckBox2ActionPerformed(java.awt.event.ActionEventevt){//TODOaddyourhandlingcodehere:JCheckBoxjCheckBox=(JCheckBox)evt.getSource();intintValue=dataset.getValue(1,1).intValue();if(jCheckBox.isSelected()){intValue++;}else{intValue--;}dataset.setValue(intValue,"张三2","张三2");}privatevoidjCheckBox3ActionPerformed(java.awt.event.ActionEventevt){//TODOaddyourhandlingcodehere:JCheckBoxjCheckBox=(JCheckBox)evt.getSource();intintValue=dataset.getValue(2,2).intValue();if(jCheckBox.isSelected()){intValue++;}else{intValue--;}dataset.setValue(intValue,"张三3","张三3");}privatevoidjCheckBox6ActionPerformed(java.awt.event.ActionEventevt){//TODOaddyourhandlingcodehere:JCheckBoxjCheckBox=(JCheckBox)evt.getSource();intintValue=dataset.getValue(5,5).intValue();if(jCheckBox.isSelected()){intValue++;}else{intValue--;}dataset.setValue(intValue,"张三6","张三6");}privatevoidjCheckBox4ActionPerformed(java.awt.event.ActionEventevt){//TODOaddyourhandlingcodehere:JCheckBoxjCheckBox=(JCheckBox)evt.getSource();intintValue=dataset.getValue(3,3).intValue();if(jCheckBox.isSelected()){intValue++;}else{intValue--;}dataset.setValue(intValue,"张三4","张三4");}privateCategoryDatasetgetDataSet(){dataset=newDefaultCategoryDataset();dataset.addValue(0,"张三1","张三1");dataset.addValue(0,"张三2","张三2");dataset.addValue(0,"张三3","张三3");dataset.addValue(0,"张三4","张三4");dataset.addValue(0,"张三5","张三5");dataset.addValue(0,"张三6","张三6");returndatas