I got two errors after I compiled my code.
The errors are:
1.
local variable input is accessed within inner class;
needs to be declared final
String name = input.getText();
2.
local variable c_age is accessed within inner class;
needs to be declared final
Object child_age = c_age.getSelectedItem();
This is my code:
import javax.swing.*;
import java.awt.event.*;
public class GUI
{
public static void main(String[] args)
{
JFrame frame = new JFrame("Try GUI");
JLabel l1 = new JLabel("Please Enter Your Child's Name");
JTextField input = new JTextField("",10);
JLabel l2 = new JLabel("Choose Your Child's Age");
String[] age = {"Age","1","2","3","4","5","6"};
JComboBox c_age = new JComboBox(age);
JButton button = new JButton("Search");
JTextArea result = new JTextArea();
JScrollPane extend_area = new JScrollPane(result);
button.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent ae)
{
String name = input.getText();
Object child_age = c_age.getSelectedItem();
}
});
JPanel panel = new JPanel();
panel.add(l1);
panel.add(input);
panel.add(l2);
panel.add(c_age);
panel.add(button);
panel.add(extend_area);
frame.add(panel);
frame.setSize(350,350);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
How can I solve this error?
You can declare the variable final, or make it an instance (or global) variable. If you declare it final, you won't be able to change it later. Any variable defined in a method and accessed by an anonymous inner class must be final.
You just need to write a class within a class. Unlike a class, an inner class can be private and once you declare an inner class private, it cannot be accessed from an object outside the class. Following is the program to create an inner class and access it.
If you want your inner class to access outer class instance variables then in the constructor for the inner class, include an argument that is a reference to the outer class instance. The outer class invokes the inner class constructor passing this as that argument.
A local inner class cannot be instantiated from outside the block where it is created in. Till JDK 7, the Local inner class can access only the final local variable of the enclosing block. However, From JDK 8, it is possible to access the non-final local variable of enclosing block in the local inner class.
You need to declare
JTextField input = new JTextField("",10);
and
JComboBox c_age = new JComboBox(age);
like this:
final JTextField input = new JTextField("",10);
final JComboBox c_age = new JComboBox(age);
This means that input
and c_age
cannot change:
Any local variable, used but not declared in an inner class must be definitely assigned before the body of the inner class.
Explanation taken from The Java Language Specification, Section - 8.1.3 Inner Classes and Enclosing Instances
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