AWT Layout is defined as the order of placement of the components in a container. This arrangement can be done by LayoutManager. AWT Layout chapter covers the following concepts:

• Introduction to LayoutManager
• Interfaces
• List of LayoutManagers

LayoutManager is responsible to arrange the components irrespective of the platform, as per the size and position required in the fixed area. LayoutManager asks every component about the space required for them in the AWT Layout to avoid the inconvenience when a window is resized. To perform this action, it calls getMinimumSize(), getMaximumSize() and getPreferredSize() methods.

Basically, there are two types of interfaces for LayoutManager.

When a container is created, a default LayoutManager is assigned such that it supports every component of that container. A new LayoutManager can be set by using the method setLayout(). Container approaches the LayoutManager by using doLayout() method to re-arrange its components. This is done after first validation of components.

There are mainly 5 commonly used LayoutManagers as shown in the below figure:

FlowLayout arranges the components from top to bottom and left to right with the preferred sizes on the screen. LEFT, CENTER, RIGHT, LEADING and TRAILING are the five constant alignment classes used by FlowLayout. This arrangement is done in rows. If a row is filled, then the control goes to the next row.

• FlowLayout is made default when used with Panels or Applets.
• By default, the gap between the components is 5 pixels.
• Component position is aligned to CENTER by default.

[java] import java.awt.*; import java.awt.event.WindowAdapter; import java.awt.event.WindowEvent; public class SPlesson extends Frame { public SPlesson() { setLayout(new FlowLayout()); for(int i = 0; i < 5; i++) { add(new Button("SPlessons " + i)); } setSize(300, 300); setVisible(true); } public static void main(String args[]) { SPlesson s = new SPlesson(); //Closing the frame s.addWindowListener ( new WindowAdapter () { public void windowClosing ( WindowEvent evt ) { System.exit(0); } }); } }[/java] Output

Grid AWT Layout arranges the components in grid cells as rows and columns. The position has to be mentioned. To have unlimited components in a certain row or column, set its size to zero.

• The arrangement is done automatically in a serial order.
• Every cell or the component is of equal size.
• The gap between the components is 0 pixels by default.

[java]import java.awt.*; import java.awt.event.WindowAdapter; import java.awt.event.WindowEvent; public class SPlesson extends Frame{ public static void main(String argv[]){ SPlesson fa=new SPlesson(); //Setup GridLayout with 2 rows and 5 columns fa.setLayout(new GridLayout(2,3)); fa.setSize(400,300); fa.setVisible(true); fa.addWindowListener ( new WindowAdapter () { public void windowClosing ( WindowEvent evt ) { System.exit(0); } }); } SPlesson(){ add(new Button("One")); add(new Button("Two")); add(new Button("Three")); add(new Button("Four")); add(new Button("Five")); add(new Button("Six")); } }[/java] Output

BorderLayout arranges the components as per the given borders(NORTH,SOUTH,EAST,WEST) and Center. This AWT Layout requires name and position to lay the components. These five spaces are expandable and are only possible by BorderLayout. Multiple components can be made fit by using this AWT Layout.

• Frame, Dialog, FileDialog, Window and Container has BorderLayoutManager as default LayoutManager.
• 0 pixels is the default gap to be maintained between the components.
• Scrolling of the screen can be done using this layout.

[java] import java.awt.BorderLayout; import java.awt.Frame; import java.awt.Button; import java.awt.Color; import java.awt.event.WindowAdapter; import java.awt.event.WindowEvent; public class SPlesson extends Frame { public SPlesson() { // set the layout setLayout(new BorderLayout()); setBackground(Color.red); // create the components Button b1 = new Button("Apple"); Button b2 = new Button("Mango"); Button b3 = new Button("Orange"); Button b4 = new Button("Grapes"); Button b5 = new Button("Fruits"); // place the components, position should be specified add(b1, "North"); add(b2, "South"); add(b3, "East"); add(b4, "West"); add(b5, "Center"); // frame creation methods setTitle("BorderLayout"); setSize(300, 300); setVisible(true); } public static void main(String args[]) { SPlesson s= new SPlesson(); s.addWindowListener ( new WindowAdapter () { public void windowClosing ( WindowEvent evt ) { System.exit(0); } }); } }[/java] Output

GridBagLayout is very flexible and consists of extendable rows & columns. Using constraints, one can position the components as per the requirement. Here, a single component can occupy multiple cells.

GridBagConstraints acts as a helper class to GridBagLayout object and is used to set the component properties. The following are GridBagConstraints:

[java]import java.awt.*; import java.awt.event.*; import java.awt.event.WindowAdapter; import java.awt.event.WindowEvent; public class SPlesson extends Frame { public SPlesson() { GridBagLayout gbl = new GridBagLayout(); GridBagConstraints gbc = new GridBagConstraints(); setLayout(gbl); Button b ; // a reference variable of Button which can be instantiated many times if reinstantiated, the earlier object is garbage collected gbc.gridx = 0; // start setting the constraints gbc.gridy = 0; gbc.gridwidth = 1; gbc.gridheight = 1; gbc.fill = GridBagConstraints.HORIZONTAL; // grows horizontally b = new Button("First"); gbl.setConstraints(b, gbc); add(b); b = new Button("Second"); gbc.gridx = 1; // gbc.gridy = 0 is taken from the previous button. If ones the the constraint is set, it will remain same in the gbl.setConstraints(b, gbc); // subsequent code, unless it is changed add(b); b = new Button("Third"); gbc.gridx = 2; gbc.gridwidth = GridBagConstraints.REMAINDER; // REMAINDER indicates to gbl.setConstraints(b, gbc); // the layout that this component is last one in the row add(b); b = new Button("Fourth"); gbc.gridx = 0; gbc.gridy = 1; gbl.setConstraints(b, gbc); add(b); b = new Button("Fifth"); gbc.gridwidth = 1; gbc.gridy = 2; gbl.setConstraints(b, gbc); add(b); b = new Button("Six"); gbc.gridx = 1; gbc.gridwidth = GridBagConstraints.REMAINDER; gbl.setConstraints(b, gbc); add(b); b = new Button("Seven"); gbc.gridx = 0; gbc.gridy = 3; gbc.gridwidth = GridBagConstraints.REMAINDER ; gbl.setConstraints(b, gbc); add(b); } public static void main(String args[]) { Frame f = new SPlesson(); f.setTitle("Creating Uneven size buttons"); f.setSize(300,300); f.setVisible(true); f.addWindowListener ( new WindowAdapter () { public void windowClosing ( WindowEvent evt ) { System.exit(0); } }); } }[/java] Output

CardLayout is used to display a single component at a time among multiple components. This layout helps in saving the space.

[java] import java.awt.*; import java.awt.event.*; import java.awt.event.WindowAdapter; import java.awt.event.WindowEvent; public class SPlesson extends Frame implements ActionListener { List tl, gl, ml, al; // 4 lists to add to a container that implements card layout Button fb, lb, nb, pb; // 4 buttons to navigate the cards of the container CardLayout cl; Panel sp, bp; // 2 panels to add lists and buttons public SPlesson() { super("Welcome to Hyderabad -- now Cyberabad"); // title to Frame tl = new List(4); // instantiate list objects gl = new List(4); ml = new List(4); al = new List(4); // popular theaters list tl.add("Sudersan complex"); tl.add("Sandhya complex"); tl.add("Odeon complex"); tl.add("Ramakrishana Estate"); tl.add("IMAX 70MM"); tl.add("Surya 35MM"); tl.add("Shanthi 70MM"); // popular gardens list gl.add("Indira Park"); gl.add("Lumbibi Park"); gl.add("Sanjivayya Park"); gl.add("Zoo Park"); gl.add("Public Gardens"); // popular monuments list ml.add("Chiran Palace"); ml.add("Falaknuma Palace"); ml.add("Charminar"); ml.add("QQ Tombs"); ml.add("Golconda Fort"); ml.add("Zuma Majid"); // popular special attractions list al.add("Birla Mandir"); al.add("Planetorium"); al.add("Hi-Tech city"); al.add("Buddha Purnima"); al.add("Ramoji Filmcity"); al.add("Shilparamam"); cl = new CardLayout(); // create a card layout object sp = new Panel(); // create a panel to add all the lists sp.setLayout(cl); // set the layout to panel, sp sp.add(tl, "t"); // add lists to panel sp.add(gl, "g"); sp.add(ml, "m"); // the string parameter is for show() later sp.add(al, "a"); // instantiate buttons fb = new Button("First Button"); lb = new Button("Last Button"); nb = new Button("Next Button"); pb = new Button("Previous Button"); bp = new Panel() ; // create a panel to add buttons bp.setLayout(new GridLayout(1, 4)); // set lay out to bp panel bp.add(fb); // add each button to panel bp.add(nb); bp.add(pb); bp.add(lb); fb.addActionListener(this); // register the buttons with listener nb.addActionListener(this); pb.addActionListener(this); lb.addActionListener(this); add(bp, "South"); // add panels to frame add(sp, "Center"); setSize(300, 300); setVisible(true) ; } public void actionPerformed(ActionEvent e) { String str = e.getActionCommand(); if(str.equals("First Button")) cl.first(sp) ; else if(str.equals("Next Button")) cl.next(sp); else if(str.equals("Previous Button")) cl.previous(sp); else if(str.equals("Last Button")) cl.last(sp); } public static void main(String args[]) { SPlesson t = new SPlesson(); t.addWindowListener ( new WindowAdapter () { public void windowClosing ( WindowEvent evt ) { System.exit(0); } }); } }[/java] Output

• LayoutManager arranges the components in the form of layouts.
• LayoutManager and LayoutManager2 are the interfaces.
• FlowLayout goes from left to right in the alignment.
• Grid cells with rows and columns are present in the GridLayout.
• BorderLayout is the default LayoutManager for Windows.
• GridBagLayout is a resizable AWT Layout.
• CardLayout outputs only a single card at a time.

Absolute positioning of components is not a good practice as it may not work well when used on different platforms that have different minimum sizes. And, the interface portability may not support the changing conditions.