填空题

本题中,在下画线上填写代码,指定变量b为字节型,变量f为单精度实型,变量l为64位整型。
public class java1
public static void main(String[] args)
______b=49;
______f=8.9f;
______1=0xfedl;
System. out. println("b="+b);
System. out. println("f="+f);
System. out. println("1="+1);

【参考答案】

第1处:byte
第2处:float
第3处:long
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填空题
本题中,通过菜单“Connect”显示一个对话框,单击“ok”按钮后,所填写的内容就会传回到主窗口并显示出来。 import java. awt. * ; import java. awt. event. * ; import javax. swing. * ; public class java3 extends JFrame implements ActionListener public java3() setTitle( java3 ); setSize(300,300); addWindowListener(new WindowAdapter() public void windowClosing(WindowEvent e) System. exit(0); ); JMenuBar mbar=new JMenuBar(); setJMenuBar(bar); JMenu fileMenu=new JMenu( File ); mbar. add(fileMenu); connectItem=new JMenuItem( Connect ); connectltem. addActionListener(this); fileMenu. add(connectItem); exitItem=new JMenuItem( Exit ); exitItem. addActionListener(this); fileMenu. add(exitItem); public void actionPerformed(ActionEvent evt) Object source=evt. getSource(); if (source==connectItem) ConnectInfo transfer=new ConnectInfo( yourname , pw ); if(dialog==null) dialog=new ConnectDialog(this); if(dialog. showDialog(transfer)) String uname=transfer. username; String pwd=transfer. password; Container contentPane=getContentPane(); contentPane. add(new JLabel( username= +uname+ , password= +pwd), South ); validate(); else if(source==exitItem) System. exit(0); public static void main(String[] args) JFrame f=new java3(); f. show(); private ConnectDialog dialog=null; private JMenuItem connectltem; private JMenuItem exitItem; class Connectlnfo public String username; public String password; public ConneetInfo(String u, String p) username=u; password=p; class ConnectDialog extends JDialog implements ActionListener public ConnectDialog() super(parent, Connect , true); Container contentPane=getContentPane(); JPanel p1=new JPanel(); p1. setLayout(new GridLayout(2,2)); p1. add(new JLabel( User name: )); p1. add(username=new JTextField( )); p1. add(new JLabel( Password: )); p1. add(password=new JPasswordField( )) contentPane. add( Center , p1); Panel p2=new Panel(); okButton=addButton(p2, Ok ); cancelButton=addButton(p2, Cancel ); contentPane. add( South , p2); setSize(240,120); JButton addButton(Container c, String name) JButton button=new JButton(name); button. addActionListener(this); c. add(button); return button; public void actionPerformed(ActionEvent evt) Object source=evt. getSource(); if(source==okButton) ok=true; setVisible(false); else if (source==cancelButton) setVisible(faIse); public void showDialog(ConnectInfo transfer) username. setText(transfer. username); password. setText(transfer. password); ok=false; show(); if(ok) transfer. username=username, getText(); transfer. password=new String(password. getPassword()); return ok; private JTextField username; private JPasswordField password; private boolean ok; private JButton okButton; private JButton cancelButton;