Design a GUI Based Application using Java Swing Controls

Explanation

This Java code demonstrates a fundamental approach to creating a Graphical User Interface (GUI) using Java's Abstract Window Toolkit (AWT). The program creates a simple window (referred to as a Frame) and places three interactive buttons inside it: "OK", "SUBMIT", and "CANCEL".

Step-by-step logic:

1. import java.awt.*;: This line brings in all the necessary classes from the AWT package, such as Frame (for the window) and Button (for the buttons).
2. class gui1 { ... }: This defines a class named gui1, which will encapsulate our GUI logic.
3. gui1() { ... }: This is the constructor of the gui1 class. When an object of gui1 is created, the code inside this constructor is automatically executed. This is where the GUI components are initialized and arranged.
4. Frame f = new Frame("Button Example");: Inside the constructor, a new Frame object is created. A Frame is a top-level window with a title bar and borders. The title of this window is set to "Button Example".
5. Button b1 = new Button("OK");: A new Button object is created with the label "OK".
6. b1.setBounds(100, 50, 80, 30);: This method is used to set the position and size of b1 manually. The arguments are (x, y, width, height). So, the "OK" button will start at x-coordinate 100, y-coordinate 50, and will be 80 pixels wide and 30 pixels tall.
7. f.add(b1);: The b1 button is added to the f frame. Without this, the button wouldn't appear in the window.
8. Button b2 = new Button("SUBMIT");, b2.setBounds(100, 100, 80, 30);, f.add(b2);: These lines repeat the process for a second button labeled "SUBMIT", placing it below the "OK" button.
9. Button b3 = new Button("CANCEL");, b3.setBounds(100, 150, 80, 30);, f.add(b3);: These lines do the same for a third button labeled "CANCEL", placing it below the "SUBMIT" button.
10. f.setSize(400, 300);: This sets the overall size of the Frame to 400 pixels wide and 300 pixels tall.
11. f.setLayout(null);: This is a crucial line. By setting the layout manager to null, we tell the frame that we will manually position and size all components using setBounds(). This is known as absolute positioning. If we didn't do this, the buttons might not appear where we intended or might stack differently based on the default layout manager.
12. f.setVisible(true);: By default, frames are invisible. This line makes the frame (and all its added components) appear on the screen.
13. public static void main(String[] args) { ... }: This is the entry point of any Java application.
14. new gui1();: Inside the main method, a new object of the gui1 class is created. This action automatically calls the gui1() constructor, which then builds and displays the GUI window with the buttons.

In essence, the code sets up a basic window and populates it with three buttons, manually arranging them in a vertical column.

Algorithm

The algorithm for creating the GUI is as follows:

1. Initialize the AWT toolkit by importing necessary classes.
2. Define a class to contain the GUI components and their setup logic.
3. Implement a constructor within this class to perform the following steps:
   • Create a top-level window (a Frame) and set its title.
   • For each desired button:
     • Create a Button object with a specified label.
     • Set the button's position and dimensions using absolute coordinates (setBounds).
     • Add the button to the Frame.
   • Set the overall size of the Frame.
   • Disable the default layout manager for the Frame to enable absolute positioning (setLayout(null)).
   • Make the Frame visible on the screen.
4. Implement the main method as the application's entry point.
5. Inside main, create an instance of the GUI class, triggering its constructor and thus initiating the GUI display.