Steps to perform Event Handling

Steps to perform Event Handling

Following steps are required to perform event handling:

1. Register the component with the Listener

Registration Methods

For registering the component with the Listener, many classes provide the registration methods. For example:

• Button
  • public void addActionListener(ActionListener a){}
• MenuItem
  • public void addActionListener(ActionListener a){}
• TextField
  • public void addActionListener(ActionListener a){}
  • public void addTextListener(TextListener a){}
• TextArea
  • public void addTextListener(TextListener a){}
• Checkbox
  • public void addItemListener(ItemListener a){}
• Choice
  • public void addItemListener(ItemListener a){}
• List
  • public void addActionListener(ActionListener a){}
  • public void addItemListener(ItemListener a){}

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Java Event Handling Code

We can put the event handling code into one of the following places:

1. Within class
2. Other class
3. Anonymous class

Java event handling by implementing ActionListener

1. import java.awt.*;  
2. import java.awt.event.*;  
3. class AEvent extends Frame implements ActionListener{  
4. TextField tf;  
5. AEvent(){  
6.   
7. //create components  
8. tf=new TextField();  
9. tf.setBounds(60,50,170,20);  
10. Button b=new Button("click me");  
11. b.setBounds(100,120,80,30);  
12.   
13. //register listener  
14. b.addActionListener(this);//passing current instance  
15.   
16. //add components and set size, layout and visibility  
17. add(b);add(tf);  
18. setSize(300,300);  
19. setLayout(null);  
20. setVisible(true);  
21. }  
22. public void actionPerformed(ActionEvent e){  
23. tf.setText("Welcome");  
24. }  
25. public static void main(String args[]){  
26. new AEvent();  
27. }  
28. }  

public void setBounds(int xaxis, int yaxis, int width, int height); have been used in the above example that sets the position of the component it may be button, textfield etc.

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2) Java event handling by outer class

1. import java.awt.*;  
2. import java.awt.event.*;  
3. class AEvent2 extends Frame{  
4. TextField tf;  
5. AEvent2(){  
6. //create components  
7. tf=new TextField();  
8. tf.setBounds(60,50,170,20);  
9. Button b=new Button("click me");  
10. b.setBounds(100,120,80,30);  
11. //register listener  
12. Outer o=new Outer(this);  
13. b.addActionListener(o);//passing outer class instance  
14. //add components and set size, layout and visibility  
15. add(b);add(tf);  
16. setSize(300,300);  
17. setLayout(null);  
18. setVisible(true);  
19. }  
20. public static void main(String args[]){  
21. new AEvent2();  
22. }  
23. }  

1. import java.awt.event.*;  
2. class Outer implements ActionListener{  
3. AEvent2 obj;  
4. Outer(AEvent2 obj){  
5. this.obj=obj;  
6. }  
7. public void actionPerformed(ActionEvent e){  
8. obj.tf.setText("welcome");  
9. }  
10. }  

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3) Java event handling by anonymous class

1. import java.awt.*;  
2. import java.awt.event.*;  
3. class AEvent3 extends Frame{  
4. TextField tf;  
5. AEvent3(){  
6. tf=new TextField();  
7. tf.setBounds(60,50,170,20);  
8. Button b=new Button("click me");  
9. b.setBounds(50,120,80,30);  
10.   
11. b.addActionListener(new ActionListener(){  
12. public void actionPerformed(){  
13. tf.setText("hello");  
14. }  
15. });  
16. add(b);add(tf);  
17. setSize(300,300);  
18. setLayout(null);  
19. setVisible(true);  
20. }  
21. public static void main(String args[]){  
22. new AEvent3();  
23. }  
24. }  

Anurag Rana