sum+=n; n++; }
while( ) System.out.println(“sum is”+sum);
System.out.println(“\\\\n******for循环******”); sum=0;
for(int i=1; i++) { sum+=i; }
System.out.println(“sum is”+sum); } }
8.设计一个窗口，上面有一个按钮。当鼠标移到按钮上时，立即隐藏该按钮；当鼠标离开按钮时，显示该按钮。请在横线处填入适当内容完成程序。
import java.awt.*;
; import javax.swing.*; public class TestEvent {
static JButton bt = new JButton(\隐藏按钮\public static void main(String[] args) {
Frame f = new Frame(); f.setLocation(300, 200); f.setSize(200,200); f.setLayout(null);
(new MouseMove()); bt.setBackground(Color.cyan);
bt.setBounds(new Rectangle(45, 100, 90, 30)); f.add(bt);
f.pack();
f.addWindowListener(new WindowAdapter() { });
f.setVisible(true);
public void windowClosing(WindowEvent e) { }
System.exit(0);
} }
class MouseMove extends MouseAdapter{
public void mouseClicked(MouseEvent e) { }
public void mouseExited(MouseEvent e) {
TestEvent.bt.setVisible(true);
;
} }
9. C
{
abstract void callme()； }
class D C
{
void callme() {
System.out.println(“重写callme()方法”)；
} }
public class Abstract {
public static void main(String args[]) {
C c= D(); c.callme();
} }
10. 下列程序实现从当前目录的date.ser文件中读取文件内容并显示出来.请将程序补充完整. import java.io.*; import java.util.Date; public class UnSerializeDate {
UnSerializeDate() {
Date d=null; try {
FileInputStream f=new _________(“date.ser”); ObjectInputStream s=new ObjectInputStream(________); d=(Date) s.readObject(); f.close(); }
catch(Exception e) {
e.printStackTrace();
}
System.out.println(“Unserialized Date object from date.set”); System.out.println(“Date:”+d); }
public static void main(String args[]) {
new UnSerializeDate(); } }
11. 下面程序分别用while 和for语句实现1~10累计求和。请在横线处填入适当内容完成程序。 Public class Sum {
public static void main(String args[]) {
System.out.println(“\\\\n*****while循环*****”); int n=10,sum=0; while( ) { sum+=n; n--; }
System.out.println(“sum is”+sum);
System.out.println(“\\\\n******for循环******”); sum=0;
for(int i =1; i++) { sum+= i; }
System.out.println(“sum is”+sum);
} }
12.设计一个窗口，上面有一个按钮。当鼠标移到按钮上时，立即隐藏该按钮；当鼠标离开按钮时，显示该按钮。请在横线处填入适当内容完成程序。
import java.awt.*;
; }
class MouseMove extends MouseAdapter{
public void mouseClicked(MouseEvent e) { }
public void mouseExited(MouseEvent e) {
;
TestEvent.bt.setVisible(false);
public class TestEvent {
static Button bt = new Button(\隐藏按钮\public static void main(String[] args) { }
Frame f1 = new Frame(); f1.setLocation(300, 300); f1.setSize(100,100);
bt.addMouseListeneer (new MouseMove()); bt.setBackground(Color.cyan);
bt.setBounds(new Rectangle(45, 100, 90, 30)); f1.add(bt);
f1.addWindowListener(new WindowAdapter() { });
f1.setVisible(true);
public void windowClosing(WindowEvent e) { }
;