Calling a JFrame class into another class

Question

 import java.awt.*;
 import java.awt.event.*;
 import javax.swing.*;

public class Temperature extends JFrame implements ActionListener{
private JLabel text1,text2;
private JTextField userInput,output;
private JButton cvrt,cvrt1,clr;

public void BuildGUI(){

    text1 = new JLabel("Key in your value");
    text2 = new JLabel("Answer");
    userInput = new JTextField();
    output = new JTextField();
    cvrt = new JButton("Convert Celcius to Fahrenheit");
    cvrt.addActionListener(this);
    cvrt1 = new JButton ("Convert Fahrenheit to Celcius");
    cvrt1.addActionListener(this);
    clr = new JButton("Clear");
    clr.addActionListener(this);

    Container cpane = getContentPane();
    cpane.setLayout(new GridLayout(4,2));
    setVisible(true);
    cpane.add(text1);
    cpane.add(userInput);
    cpane.add(text2);
    cpane.add(output);
    cpane.add(cvrt);
    cpane.add(cvrt1);
    cpane.add(clr);   
}

public void actionPerformed(ActionEvent e){
     double fahrenheit,celcius;
    if(e.getSource()== cvrt){
        String value = userInput.getText();
        celcius = Double.parseDouble(value);
        fahrenheit = celcius*1.8+32;
         String out = ""+fahrenheit;     
         output.setText(out);
    }else if (e.getSource()== cvrt1){
        String value = userInput.getText();
        fahrenheit = Double.parseDouble(value);
        celcius = (fahrenheit-32)/1.8;
        String out = ""+ celcius;
        output.setText(out);
    }else{
        userInput.setText(null);
        output.setText(null);
    }
}
}

Sorry I'm still new to Java. I Was given an assignment to create a tabbedpane. I'm Just Wondering can you call up the class above into the JTabbed Pane below? Because it will be a mess to throw every codes in a class. Been running through a lot of website but still in vain. Hopefully someone can point it.

public class Windows extends JFrame{
public Windows(){
    setTitle("Converter");       
    setSize(null);
    JTabbedPane tabby = new JTabbedPane();
    getContentPane().add(tabby);

}

Answer 1

Your class Temperature has to be a JPanel and you have to create a suituable constructor, which initializes your GUI. Then you could add the JPanel to your JTabbedPane in another class like this:

public class Windows extends JFrame{
public Windows(){
    setTitle("Converter");       
    setSize(null);
    JTabbedPane tabby = new JTabbedPane();
    getContentPane().add(tabby);
    Temperature t = new Temperature();
    tabby.addTab(t);
}

Answer 2

Ok first of all:
Why the size of JFrame is null?
How can you see something which isn't visible???
Use the method JFrame.setSize(width,height) [ Link ]

Second thing is :
There is a method called JFrame.setVisible(boolean) [ Link ] , have you ever thought why that method is provided?
To make the JFrame Visible ofcourse.

Another Thing is:
There is a method called setDefaultCloseOperation(int value) [ Link ], which defines what to do when JFrame is closed, use this. Here is the Code:

public class Windows extends JFrame{
public Windows(){
    setTitle("Converter");       
    setSize(100,200);
    JTabbedPane tabby = new JTabbedPane();
    getContentPane().add(tabby);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    setVisible(true);

}

Refer Oracle Java docs for rest of the methods:
http://docs.oracle.com/javase/6/docs/api/javax/swing/JFrame.html

AND Finally :
Even with my revised code you won't see tabbed pane correctly because you have to use
LAYOUT MANAGERS [ Link ] inside the JFrame to align,fix and position the Components.