• Calculator using 200X300 size panel
  
• Calculator using 300X300 size panel
  
• Calculator using 640X480 size panel
  

import java.awt.*;
import java.awt.event.*;
import java.applet.*;

public class Calculator extends Applet {

  private TextField textField;
  private Button[] numButton;
  private GridBagLayout gbLayout;
  private GridBagConstraints gbConstraints;

  // Add a component to the container
  private void addComp(Component c, GridBagLayout gbLayout,
                       GridBagConstraints gbConstraints,
                       int row, int column, int numRows,
                       int numColumns, int weightx, int weighty) {

    // Set parameters
    gbConstraints.gridx = column;
    gbConstraints.gridy = row;
    gbConstraints.gridwidth = numColumns;
    gbConstraints.gridheight = numRows;
    gbConstraints.weightx = weightx;
    gbConstraints.weighty = weighty;

    // Set constraints in the GridBagLayout
    gbLayout.setConstraints(c, gbConstraints);

    // Add component to the container
    add(c);
  }

  public void init() {

    // Initialize GUI components
    textField  = new TextField(" ");
    numButton = new Button[10];
    for (int i = 0; i < 10; i++) 
	numButton[i] = new Button(i+"");

    // Create GridBagLayout and GridBagConstraints object
    gbLayout = new GridBagLayout();
    gbConstraints = new GridBagConstraints();
    setLayout(gbLayout);

    gbConstraints.fill = GridBagConstraints.BOTH;

    //add components
    addComp(textField, gbLayout, gbConstraints,    0, 0, 1, 3, 100, 100);
    addComp(numButton[7], gbLayout, gbConstraints, 1, 0, 1, 1, 100, 100);
    addComp(numButton[8], gbLayout, gbConstraints, 1, 1, 1, 1, 100, 100);
    addComp(numButton[9], gbLayout, gbConstraints, 1, 2, 1, 1, 100, 100);
    addComp(numButton[4], gbLayout, gbConstraints, 2, 0, 1, 1, 100, 100);
    addComp(numButton[5], gbLayout, gbConstraints, 2, 1, 1, 1, 100, 100);
    addComp(numButton[6], gbLayout, gbConstraints, 2, 2, 1, 1, 100, 100);
    addComp(numButton[1], gbLayout, gbConstraints, 3, 0, 1, 1, 100, 100);
    addComp(numButton[2], gbLayout, gbConstraints, 3, 1, 1, 1, 100, 100);
    addComp(numButton[3], gbLayout, gbConstraints, 3, 2, 1, 1, 100, 100);
    addComp(numButton[0], gbLayout, gbConstraints, 4, 0, 1, 3, 100, 100);
  }
}