Layout in Java Desktop Application

In general, layout managers are objects used in widget toolkits that have the ability to arrange widgets by their relative positions. Java uses layout managers to arrange components in a consistent manner across all windowing platforms.

In this section, we will introduce the following Swing layout managers:

Layout Manager	Description
FlowLayout	Objects that arrange components in a directional flow, much like lines of text in a paragraph.
GridLayout	Objects that divide the container into equal-sized rectangles and arrange each component into one of these cells.
BorderLayout	Objects that arrange components to the top, bottom, left, right, and center of a container.

To demonstrate these layout managers, we will create an Applet that allows the user to select a layout manager from a list and see the effects it has on some Swing components. In this implementation, we use a BorderLayout manager to place a drop-down list above a panel that contains serveral Swing components (buttons). When an item in the drop-down list is selected, the layout manager for the panel is changed, and without explicitly setting the bounds of any components, the layout manager rearranges the buttons.

Setting Maximum no. of characters in jTextField for Swing Application

Sometimes we need to fixed the maximum size of a text field. For this purpose, we need to implement a document containing an overriding function of plain document.

public class MaxLengthTextDocument extends PlainDocument {

private int maxChars;

@Override
public void insertString(int offs, String str, AttributeSet a)
throws BadLocationException {
if(str != null && (getLength() + str.length() < getMaxChars())){ super.insertString(offs, str, a); } } /** * @return the maxChars */ public int getMaxChars() { return maxChars; } /** * @param maxChars the maxChars to set */ public void setMaxChars(int maxChars) { this.maxChars = maxChars; } }

after that we will have to set the following line after initComponents() of view file.

MaxLengthTextDocument maxLength = new MaxLengthTextDocument();
maxLength.setMaxChars(12);//50 is a maximum number of character
this.txtMobileNo.setDocument(maxLength);