Java2实用教程（第5版）最新答案-耿祥义

Scanner scanner = new Scanner(cost); scanner.useDelimiter(\ double sum=0; int count =0;

while(scanner.hasNext()){

try{ double score = scanner.nextDouble(); count++; sum = sum+score; System.out.println(score); }

catch(InputMismatchException exp){ String t = scanner.next(); } }

System.out.println(\总分:\分\ System.out.println(\平均分:\分\ } }

习题九（第9章）

一、问答题

1．Frame容器的默认布局是BorderLayout布局。 2．不可以。

3．ActionEvent。 4．DocumentEvent。 5．5个。

6．MouseMotionListener。 二、选择题

1．C。2．A。3．A。4．D。5．C。 三、编程题

1． import java.awt.*;

import javax.swing.event.*; import javax.swing.*; import java.awt.event.*; public class E {

public static void main(String args[]) { Computer fr=new Computer(); } }

class Computer extends JFrame implements DocumentListener {

JTextArea text1,text2; int count=1;

double sum=0,aver=0; Computer() {

setLayout(new FlowLayout()); text1=new JTextArea(6,20); text2=new JTextArea(6,20); add(new JScrollPane(text1)); add(new JScrollPane(text2)); text2.setEditable(false);

(text1.getDocument()).addDocumentListener(this); setSize(300,320); setVisible(true); validate();

setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); }

public void changedUpdate(DocumentEvent e) { String s=text1.getText();

String []a =s.split(\ sum=0; aver=0;

for(int i=0;i

try { sum=sum+Double.parseDouble(a[i]); }

catch(Exception ee) {} }

aver=sum/count; text2.setText(null); text2.append(\和:\ text2.append(\平均值:\ }

public void removeUpdate(DocumentEvent e){ changedUpdate(e); }

public void insertUpdate(DocumentEvent e){ changedUpdate(e); } }

2. import java.awt.*;

import javax.swing.event.*; import javax.swing.*; import java.awt.event.*; public class E {

public static void main(String args[]) {

ComputerFrame fr=new ComputerFrame(); } }

class ComputerFrame extends JFrame implements ActionListener { JTextField text1,text2,text3;

JButton buttonAdd,buttonSub,buttonMul,buttonDiv; JLabel label;

public ComputerFrame() { setLayout(new FlowLayout()); text1=new JTextField(10); text2=new JTextField(10); text3=new JTextField(10);

label=new JLabel(\ label.setBackground(Color.green); add(text1); add(label); add(text2); add(text3);

buttonAdd=new JButton(\加\ buttonSub=new JButton(\减\ buttonMul=new JButton(\乘\ buttonDiv=new JButton(\除\ add(buttonAdd); add(buttonSub); add(buttonMul); add(buttonDiv);

buttonAdd.addActionListener(this); buttonSub.addActionListener(this); buttonMul.addActionListener(this); buttonDiv.addActionListener(this); setSize(300,320); setVisible(true); validate();

setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); }

public void actionPerformed(ActionEvent e) { double n;

if(e.getSource()==buttonAdd) { double n1,n2;

try{ n1=Double.parseDouble(text1.getText()); n2=Double.parseDouble(text2.getText()); n=n1+n2;

text3.setText(String.valueOf(n)); label.setText(\

}

catch(NumberFormatException ee) { text3.setText(\请输入数字字符\ } }

else if(e.getSource()==buttonSub) { double n1,n2;

try{ n1=Double.parseDouble(text1.getText()); n2=Double.parseDouble(text2.getText()); n=n1-n2;

text3.setText(String.valueOf(n)); label.setText(\ }

catch(NumberFormatException ee) { text3.setText(\请输入数字字符\ } }

else if(e.getSource()==buttonMul) {double n1,n2;

try{ n1=Double.parseDouble(text1.getText()); n2=Double.parseDouble(text2.getText()); n=n1*n2;

text3.setText(String.valueOf(n)); label.setText(\ }

catch(NumberFormatException ee) { text3.setText(\请输入数字字符\ } }

else if(e.getSource()==buttonDiv) {double n1,n2;

try{ n1=Double.parseDouble(text1.getText()); n2=Double.parseDouble(text2.getText()); n=n1/n2;

text3.setText(String.valueOf(n)); label.setText(\ }

catch(NumberFormatException ee) { text3.setText(\请输入数字字符\ } } validate(); } }