AWT Layouts

Layout means the arrangement of components within the container. The task of layouting the controls is done automatically by the Layout Manager.

The Java LayoutManagers helps to control the positioning and size of the components in GUI forms. LayoutManager is an interface that is implemented by all the classes of layout managers.

The layout manager is associated with every Container object. Each layout manager is an object of the class that implements the LayoutManager interface.

There are the following classes that represent the layout managers:

1. java.awt.BorderLayout
2. java.awt.FlowLayout
3. java.awt.GridLayout
4. java.awt.CardLayout
5. java.awt.GridBagLayout

1. Border Layout:

The borderlayout arranges the components to fit in the five regions: east, west, north, south and center.

Each region (area) may contain one component only. It is the default layout of a frame or window. The BorderLayout provides five constants for each region:

1. public static final int NORTH
2. public static final int SOUTH
3. public static final int EAST
4. public static final int WEST
5. public static final int CENTER

Constructors of BorderLayout class:

• BorderLayout(): creates a border layout but with no gaps between the components.
• BorderLayout(int hgap, int vgap): creates a border layout with the given horizontal and vertical gaps between the components.

Ex:

import java.awt.*;   

import javax.swing.*;     

public class Border  

{   

JFrame f;   

Border() 

{   

    f = new JFrame();   

     // creating buttons 

    JButton b1 = new JButton("NORTH");; // the button will be labeled as NORTH  

    JButton b2 = new JButton("SOUTH");; // the button will be labeled as SOUTH 

    JButton b3 = new JButton("EAST");; // the button will be labeled as EAST 

    JButton b4 = new JButton("WEST");; // the button will be labeled as WEST 

    JButton b5 = new JButton("CENTER");; // the button will be labeled as CENTER 

    f.add(b1, BorderLayout.NORTH); // b1 will be placed in the North Direction   

    f.add(b2, BorderLayout.SOUTH);  // b2 will be placed in the South Direction   

    f.add(b3, BorderLayout.EAST);  // b2 will be placed in the East Direction   

    f.add(b4, BorderLayout.WEST);  // b2 will be placed in the West Direction   

    f.add(b5, BorderLayout.CENTER);  // b2 will be placed in the Center    

    f.setSize(300, 300);   

    f.setVisible(true);   

}   

public static void main(String[] args) {   

    new Border();   

}   

}   

2. Flow Layout

It layouts the components in a directional flow. The Java FlowLayout class is used to arrange the components in a line, one after another (in a flow). It is the default layout of the applet or panel.

Fields of FlowLayout class

1. public static final int LEFT
2. public static final int RIGHT
3. public static final int CENTER
4. public static final int LEADING
5. public static final int TRAILING

Constructors of FlowLayout class

1. FlowLayout(): creates a flow layout with centered alignment and a default 5 unit horizontal and vertical gap.
2. FlowLayout(int align): creates a flow layout with the given alignment and a default 5 unit horizontal and vertical gap.
3. FlowLayout(int align, int hgap, int vgap): creates a flow layout with the given alignment and the given horizontal and vertical gap.

Ex:

// import statements 

import java.awt.*;   

import javax.swing.*;       

public class FlowLayoutExample 

{  

JFrame frameObj; 

// constructor   

FlowLayoutExample() 

{   

    // creating a frame object 

    frameObj = new JFrame();   

     // creating the buttons 

    JButton b1 = new JButton("1");   

    JButton b2 = new JButton("2");   

    JButton b3 = new JButton("3");   

    JButton b4 = new JButton("4");   

    JButton b5 = new JButton("5");     

    // adding the buttons to frame       

    frameObj.add(b1); frameObj.add(b2); frameObj.add(b3); frameObj.add(b4);     

    frameObj.add(b5);

     // parameter less constructor is used therefore, alignment is center  

    // horizontal as well as the vertical gap is 5 units. 

    frameObj.setLayout(new FlowLayout());   

    frameObj.setSize(300, 300);   

    frameObj.setVisible(true);   

}  

// main method 

public static void main(String argvs[])  

{   

    new FlowLayoutExample();   

}   

}  

3. Grid Layout

The GridLayout manages the components in form of a rectangular grid. The Java GridLayout class is used to arrange the components in a rectangular grid. One component is displayed in each rectangle.

Constructors of GridLayout class

1. GridLayout(): creates a grid layout with one column per component in a row.
2. GridLayout(int rows, int columns): creates a grid layout with the given rows and columns but no gaps between the components.
3. GridLayout(int rows, int columns, int hgap, int vgap): creates a grid layout with the given rows and columns along with given horizontal and vertical gaps.

Ex:

/ import statements 

import java.awt.*;   

import javax.swing.*;      

public class GridLayoutExample 

{   

JFrame frameObj;   

// constructor 

GridLayoutExample() 

{   

frameObj = new JFrame();   

JButton btn1 = new JButton("1");   

JButton btn2 = new JButton("2");   

JButton btn3 = new JButton("3");   

JButton btn4 = new JButton("4");   

JButton btn5 = new JButton("5");   

// adding buttons to the frame 

// since, we are using the parameterless constructor, therfore;  

// the number of columns is equal to the number of buttons we  

// are adding to the frame. The row count remains one. 

frameObj.add(btn1); frameObj.add(btn2); frameObj.add(btn3); 

frameObj.add(btn4); frameObj.add(btn5);

 // setting the grid layout using the parameterless constructor   

frameObj.setLayout(new GridLayout());   

frameObj.setSize(300, 300);   

frameObj.setVisible(true);   

} 

// main method 

public static void main(String argvs[])  

{   

new GridLayoutExample();   

}   

}

4. Card Layout

The CardLayout object treats each component in the container as a card. Only one card is visible at a time.

Constructors of CardLayout Class

1. CardLayout(): creates a card layout with zero horizontal and vertical gap.
2. CardLayout(int hgap, int vgap): creates a card layout with the given horizontal and vertical gap.

Commonly Used Methods of CardLayout Class

• public void next(Container parent): is used to flip to the next card of the given container.
• public void previous(Container parent): is used to flip to the previous card of the given container.
• public void first(Container parent): is used to flip to the first card of the given container.
• public void last(Container parent): is used to flip to the last card of the given container.
• public void show(Container parent, String name): is used to flip to the specified card with the given name.

Ex:

import java.awt.*;   

import javax.swing.*;  

import java.awt.event.*;   

public class CardLayoutExample1 extends JFrame implements ActionListener 

{   

CardLayout crd;   

// button variables to hold the references of buttons 

JButton btn1, btn2, btn3;   

Container cPane;  

// constructor of the class 

CardLayoutExample1() 

{   

 cPane = getContentPane();   

 //default constructor used therefore, components will cover the whole area 

crd = new CardLayout();   

cPane.setLayout(crd);   

// creating the buttons 

btn1 = new JButton("Apple");   

btn2 = new JButton("Boy");   

btn3 = new JButton("Cat");   

// adding listeners to it 

btn1.addActionListener(this);   

btn2.addActionListener(this);   

btn3.addActionListener(this);   

cPane.add("a", btn1); // first card is the button btn1 

cPane.add("b", btn2); // first card is the button btn2 

cPane.add("c", btn3);  // first card is the button btn3            

}   

public void actionPerformed(ActionEvent e)  

{   

// Upon clicking the button, the next card of the container is shown 

// after the last card, again, the first card of the container is shown upon clicking 

crd.next(cPane);   

}   

// main method 

public static void main(String argvs[])  

{    

// creating an object of the class CardLayoutExample1 

CardLayoutExample1 crdl = new CardLayoutExample1();  

// size is 300 * 300         

crdl.setSize(300, 300);   

crdl.setVisible(true);   

crdl.setDefaultCloseOperation(EXIT_ON_CLOSE);   

}   

} 

5. GridBag Layout

This is the most flexible layout manager class.The object of GridBagLayout aligns the component vertically,horizontally or along their baseline without requiring the components of same size. Each GridBagLayout object maintains a dynamic, rectangular grid of cells. Each component occupies one or more cells known as its display area.

The GridBagLayout manages each component's minimum and preferred sizes in order to determine the component's size. GridBagLayout components are also arranged in the rectangular grid but can have many different sizes and can occupy multiple rows or columns.

Constructor:

GridBagLayout(): The parameterless constructor is used to create a grid bag layout manager.

Ex:

import java.awt.Button; 

import java.awt.GridBagConstraints; 

import java.awt.GridBagLayout; 

import javax.swing.*; 

public class GridBagLayoutExample extends JFrame{ 

    public static void main(String[] args) { 

            GridBagLayoutExample a = new GridBagLayoutExample(); 

        } 

        public GridBagLayoutExample() { 

    GridBagLayoutgrid = new GridBagLayout(); 

            GridBagConstraints gbc = new GridBagConstraints(); 

            setLayout(grid); 

            setTitle("GridBag Layout Example"); 

            GridBagLayout layout = new GridBagLayout(); 

    this.setLayout(layout); 

    gbc.fill = GridBagConstraints.HORIZONTAL; 

    gbc.gridx = 0; 

    gbc.gridy = 0; 

    this.add(new Button("Button One"), gbc); 

    gbc.gridx = 1; 

    gbc.gridy = 0; 

    this.add(new Button("Button two"), gbc); 

    gbc.fill = GridBagConstraints.HORIZONTAL; 

    gbc.ipady = 20; 

    gbc.gridx = 0; 

    gbc.gridy = 1; 

    this.add(new Button("Button Three"), gbc); 

    gbc.gridx = 1; 

    gbc.gridy = 1; 

    this.add(new Button("Button Four"), gbc); 

    gbc.gridx = 0; 

    gbc.gridy = 2; 

    gbc.fill = GridBagConstraints.HORIZONTAL; 

    gbc.gridwidth = 2; 

    this.add(new Button("Button Five"), gbc); 

            setSize(300, 300); 

            setPreferredSize(getSize()); 

            setVisible(true); 

            setDefaultCloseOperation(EXIT_ON_CLOSE); 

        } 

}