AWT-Abstract Window Toolkit

Class Checkbox

• It is used to create a Checkbox as well as radiobutton.

• Checkbox()
• Creates a check box with an empty string for its label.
For ex: chk=new Checkbox();
• Checkbox(String label)
• Creates a check box with the specified label.
For ex: chk=new Checkbox("Married");
• Checkbox(String label, boolean state)
• Creates a check box with the specified label and sets the specified state.
For ex: chk=new Checkbox("Married",true);

• Checkbox(String label, boolean state, CheckboxGroup group)
• Constructs a RadioButon with the specified label, set to the specified state.
• It adds it in the specified check box group.
For ex:
rb1=new Checkbox("Male",false,cbg);
rb2=new Checkbox("Female",false,cbg);

• boolean getState()
• Return current state of check box.
For ex:boolean b=chk.getState();
• void setState(boolean state)
• Sets the state of this check box.
For ex: chk.setState(false);
• String getLabel()
• Gets the label of this check box.
For ex:String lbl=chk.getLabel();
• void setLabel(String label)
• Sets this check box's label.
For ex:chk.setLabel("Single");
• void addItemListener(ItemListener l)
• Adds the specified item listener to receive item events from this check box
• Due to this notification will be send to listener x by calling its special method itemStateChanged.
For ex:chk.addItemListener(x);

Interface ItemListener [ java.awt.event]

• The Listener Object that is interested in processing a Checkbox event must implements this interface.

• void itemStateChanged(ItemEvent e)
• Invoked when an item has been selected or deselected by the user.

 import java.applet.*;
 import java.awt.*;
 import java.awt.event.*;
 class MyFrame extends Frame 
 implements ActionListener
 {
    Label lbl,lbl2;
    TextField txt;
    Checkbox c1,c2,c3;
    Button btn;
    public MyFrame()
    {
        setLayout(new FlowLayout());
        lbl=new Label("Basic Salary");
        Checkbox("Add Bonus Rs 3000");
        add(c1);
        c2=new Checkb add(lbl);
        txt=new TextField(10);
        add(txt);
        c1=new ox("Add HRA rs 2000");
        add(c2);
        c3=new Checkbox("Deduct ITax Rs 2500");
        add(c3);
        btn=new Button("Net Salary"); 
        add(btn);
        btn.addActionListener(this);
        lbl2=new Label();
        add(lbl2);
    }
    public void actionPerformed(ActionEvent e)
    {
        String num=txt.getText();
        int bs=Integer.parseInt(num);
        if(c1.getState())
            bs=bs+3000;
        if(c2.getState())
            bs=bs+2000;
        if(c3.getState())
            bs=bs-2500;
        lbl2.setText("Net Salary is Rs "+bs);
    }
 }
 class demo
 {
    public static void main(String args[])
    {
        MyFrame frm=new MyFrame();
        frm.setVisible(true);
        frm.setSize(400,300);
    }
 }

Class CheckboxGroup

• The object of CheckboxGroup class is used to group together a set of Checkbox to create RadioButtons.
• At a time only one check box from CheckboxGroup is allowed to be in "on" state.

• Checkbox getSelectedCheckbox()
• Gets the currently selected Checkbox from the check box group.

 import java.applet.Applet;
 import java.awt.*;
 import java.awt.event.*;
 public class MyApplet extends Applet implements ItemListener
 {
    Checkbox c1,c2,c3;
    CheckboxGroup cbg;
    public void init()
    {
        cbg=new CheckboxGroup();
        c1=new Checkbox("Red",false,cbg);
        add(c1);
        c2=new Checkbox("Green",false,cbg);
        add(c2);
        c3=new Checkbox("Blue",false,cbg);
        add(c3);
        c1.addItemListener(this);
        c2.addItemListener(this);
        c3.addItemListener(this);
    }
    public void itemStateChanged(ItemEvent e)
    {
        repaint();
    }
    public void paint(Graphics g)
    {
        if(c1.getState())
            g.setColor(Color.red);
        if(c2.getState())
            g.setColor(Color.green);
        if(c3.getState())
            g.setColor(Color.blue);
        g.fillOval(50,50,100,100);
 }
}
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