Specialised Components

J McQuillan SE204:2004/2005: Lecture 3 Slide 1

Specialised ComponentsCan create specialised components. Do this by subclassing the component that you are interested in. It now looks and behaves like we want. This subclass has all the properties of its superclass along with the extra’s we’ve added. We can now re-use this component!

can create multiple instances of it can subclass it


import java.awt.*;import javax.swing.*;class DaysPanel extends JPanel{

JComboBox days;JLabel l;

DaysPanel(){setPreferredSize(new Dimension(300, 200));setBackground(Color.white);l = new JLabel("Choose a day");days = new JComboBox();days.addItem(“Monday");days.addItem(“Tuesday");add(l);add(days);

}}


We can now place this in a frame, in an applet,

or any other higher-level container!


Other Component MethodssetVisible(boolean b)

can be called on any component it makes the component visible or invisible

setEnable(boolean b) can be used to disable a component, it

cannot receive user input most components when disabled change

their appearance


Laying out componentsCan place components in containers by

use of absolute position and size co-ordinates use of layout managers

The arrangement of several components in acontainer is called a layout.


Laying out componentsThere are a number of predefined layout classes

FlowLayout BorderLayout GridLayout GridBagLayout CardLayout

These all implement the LayoutManagerinterface


Using Layouts

Set the layout of the container by invoking the

setLayout() method.

This method accepts as a parameter an instance of a class that implements the

layoutmanager interface.


Border Layout This allows you to place components in

five different regions in the container - North, South, East, West and Center.

You specify the position of each component when adding it to the container.


Border Layout

Constructors

BorderLayout() -- creates a new border layout

BorderLayout(int hGap, int vGap) -- creates a new border layout with the specified horizontal and vertical gaps


import java.awt.*;

import javax.swing.*;

Public class borderPanel extends JPanel{

JButton[] b;

borderPanel(){

setPreferredSize(new Dimension(300, 200));

setBackground(Color.white);

setLayout(new BorderLayout());

b = new JButton[5];

for(int i=1; i<=b.length; i++)

b[i-1] = new JButton("Button "+i);

add("North", b[0]);

add("East", b[1]);

add("South", b[2]);

add("West", b[3]);

add("Center", b[4]);}

}


public class borderFrame extends JFrame

{

private borderPanel p1;

borderFrame(){

super("Border Frame");

p1 = new borderPanel();

getContentPane().add(p1);

pack();

setVisible(true);

}

public static void main(String args[]){

new borderFrame();

}

}


Flow Layout This allows any number of components

in a container.

It arranges the components from left to right in a row. When that row is full, it will begin a new row.


Flow LayoutConstructors

FlowLayout() -- creates a new flow layout with centered alignment.FlowLayout(int alignment) -- creates a new flow layout with the specified alignment.FlowLayout(int alignment, int hGap, int vGap) --creates a new flow layout with the specified alignment and horizontal and vertival gaps.


import java.awt.*;


class flowPanel extends JPanel{

JButton[] b;

int n;

flowPanel(int n){

this.n = n;



setLayout(new FlowLayout());

b = new JButton[n];

for(int i=1; i<=b.length; i++){


add(b[i-1]);

}

}

}


public class flowFrame extends JFrame {

private flowPanel p1;

flowFrame(){

super("Flow Frame");

p1 = new flowPanel(5);


pack();

setVisible(true);

}


new flowFrame();

}

}


Grid Layout This allows you to lay out components

in a grid of rows and columns.


Grid LayoutConstructors

GridLayout(int rows, int cols) -- creates a new grid layout with the specified number of rows and columns

GridLayout(int rows, int cols, int hGap, int vGap) -- creates a new grid layout with the specified number of rows and columns and specified horizontal and vertical gaps


import java.awt.*;


class gridPanel extends JPanel{

JButton[] b;

int n;

gridPanel(int n){

this.n = n;



setLayout(new GridLayout(3,2));

b = new JButton[n];

for(int i=1; i<=b.length; i++){


add(b[i-1]);

}

}

}


public class gridFrame extends JFrame {

private gridPanel p1;

gridFrame(){

super("Grid Frame");

p1 = new gridPanel(5);


pack();

setVisible(true);

}


new gridFrame();

}


Other Layouts There are other layouts available

These include CardLayout, BoxLayout

Specialised Components

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