Thread in Java - core java notes ~ foundjava

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Synchronization in Java - core java notes ~ foundjava

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MySQL Database and Java Desktop GUI Part 1 - core java notes ~ foundjava

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Java StringBuffer class - core java notes ~ foundjava

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Java String - core java notes ~ foundjava

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Java nio Tutorial with Examples - core java notes ~ foundjava

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Java Command Line Arguments - core java notes ~ foundjava

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Java Collection Framework - core java notes ~ foundjava

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Input and Output in Java - core java notes ~ foundjava

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Final Keyword In Java - core java notes ~ foundjava

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Pointers as Value parameters code in java ~ java help

import java.awt.Rectangle;

public class ObjectVarsAsParameters
{ public static void main(String[] args)
 { go();
 }
 
 public static void go()
 { Rectangle r1 = new Rectangle(0,0,5,5);
  System.out.println("In method go. r1 " + r1 + "\n");
  // could have been 
  //System.out.prinltn("r1" + r1.toString());
  r1.setSize(10, 15);
  System.out.println("In method go. r1 " + r1 + "\n");
  alterPointee(r1);
  System.out.println("In method go. r1 " + r1 + "\n");
  
  alterPointer(r1);
  System.out.println("In method go. r1 " + r1 + "\n");
 }
 
 public static void alterPointee(Rectangle r)
 { System.out.println("In method alterPointee. r " + r + "\n");
  r.setSize(20, 30);
  System.out.println("In method alterPointee. r " + r + "\n");
 }
 
 public static void alterPointer(Rectangle r)
 { System.out.println("In method alterPointer. r " + r + "\n");
  r = new Rectangle(5, 10, 30, 35);
  System.out.println("In method alterPointer. r " + r + "\n");
 }
 
 
}

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ScrollPaneLayout in java ~ java help

The layout manager used by JScrollPane. JScrollPaneLayout is responsible for nine components: a viewport, two scrollbars, a row header, a column header, and four "corner" components.

Nested Class

Modifier and Type	Class	Description
static class	ScrollPaneLayout.UIResource	It is UI resource version of ScrollPaneLayout.

Field

Modifier and Type	Field	Description
protected JViewport	colHead	It is column header child.
protected JScrollBar	hsb	It is scrollpane's horizontal scrollbar child.
protected int	hsbPolicy	It displays policy for the horizontal scrollbar.
protected Component	lowerLeft	This displays the lower left corner.
protected Component	lowerRight	This displays in the lower right corner.
protected JViewport	rowHead	It is row header child.
protected Component	upperLeft	This component displays in the upper left corner.
protected Component	upperRight	This component displays in the upper right corner.
protected JViewport	viewport	It is scrollpane's viewport child.
protected JScrollBar	vsb	It is scrollpane's vertical scrollbar child.
protected int	vsbPolicy	It is the display policy for the vertical scrollbar.

Useful methods

Modifier and Type	Method	Description
void	addLayoutComponent(String s, Component c)	It adds the specified component to the layout.
protected Component	addSingletonComponent(Component oldC, Component newC)	It removes an existing component.
JViewport	getColumnHeader()	It returns the JViewport object that is the column header.
Component	getCorner(String key)	It returns the Component at the specified corner.
JScrollBar	getHorizontalScrollBar()	It returns the JScrollBar object that handles horizontal scrolling.
int	getHorizontalScrollBarPolicy()	It returns the horizontal scrollbar-display policy.
JViewport	getRowHeader()	It returns the JViewport object that is the row header.
JScrollBar	getVerticalScrollBar()	It returns the JScrollBar object that handles vertical scrolling.
int	getVerticalScrollBarPolicy()	It returns the vertical scrollbar-display policy.
JViewport	getViewport()	It returns the JViewport object that displays the scrollable contents.

Example:

1. import javax.swing.ImageIcon;  
2. import javax.swing.JFrame;  
3. import javax.swing.JLabel;  
4. import javax.swing.JScrollPane;  
5. public class ScrollPaneDemo extends JFrame  
6. {  
7. public ScrollPaneDemo() {  
8. super("ScrollPane Demo");  
9. ImageIcon img = new ImageIcon("child.png");  
10.   
11. JScrollPane png = new JScrollPane(new JLabel(img));  
12.   
13. getContentPane().add(png);  
14. setSize(300,250);  
15. setVisible(true);  
16. }  
17.   
18. public static void main(String[] args) {  
19. new ScrollPaneDemo();  
20. }  
21. }  

Output:

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SpringLayout in java ~ java help

Java SpringLayout

A SpringLayout arranges the children of its associated container according to a set of constraints.Constraints are nothing but horizontal and vertical distance between two component edges. Every constrains are represented by a SpringLayout.Constraint object.

Each child of a SpringLayout container, as well as the container itself, has exactly one set of constraints associated with them.

Each edge position is dependent on the position of the other edge. If a constraint is added to create new edge than the previous binding is discarded. SpringLayout doesn't automatically set the location of the components it manages.

Nested Classes

Modifier and Type	Class	Description
static class	SpringLayout.Constraints	It is a Constraints object helps to govern component's size and position change in a container that is controlled by SpringLayout

Fields

Modifier and Type	Field	Description
static String	BASELINE	It specifies the baseline of a component.
static String	EAST	It specifies the right edge of a component's bounding rectangle.
static String	HEIGHT	It specifies the height of a component's bounding rectangle.
static String	HORIZONTAL_CENTER	It specifies the horizontal center of a component's bounding rectangle.
static String	NORTH	It specifies the top edge of a component's bounding rectangle.
static String	SOUTH	It specifies the bottom edge of a component's bounding rectangle.
static String	VERTICAL_CENTER	It specifies the vertical center of a component's bounding rectangle.
static String	WEST	It specifies the left edge of a component's bounding rectangle.
static String	WIDTH	It specifies the width of a component's bounding rectangle.

Useful Methods

Modifier and Type	Method	Description
void	addLayoutComponent(Component component, Object constraints)	If constraints is an instance of SpringLayout. Constraints, associates the constraints with the specified component.
void	addLayoutComponent(String name, Component c)	Has no effect, since this layout manager does not use a per-component string.
Spring	getConstraint(String edgeName, Component c)	It returns the spring controlling the distance between the specified edge of the component and the top or left edge of its parent.
SpringLayout.Constraints	getConstraints(Component c)	It returns the constraints for the specified component.
float	getLayoutAlignmentX(Container p)	It returns 0.5f (centered).
float	getLayoutAlignmentY(Container p)	It returns 0.5f (centered).
void	invalidateLayout(Container p)	It Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.
void	layoutContainer(Container parent)	It lays out the specified container.
Dimension	maximumLayoutSize(Container parent)	It is used to calculates the maximum size dimensions for the specified container, given the components it contains.
Dimension	minimumLayoutSize(Container parent)	It is used to calculates the minimum size dimensions for the specified container, given the components it contains.
Dimension	preferredLayoutSize(Container parent)	It is used to calculates the preferred size dimensions for the specified container, given the components it contains.

Example

1. import java.awt.Container;  
2. import javax.swing.JFrame;  
3. import javax.swing.JLabel;  
4. import javax.swing.JTextField;  
5. import javax.swing.SpringLayout;  
6. public class MySpringDemo {  
7.      private static void createAndShowGUI() {  
8.             JFrame frame = new JFrame("MySpringDemp");  
9.             frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
10.   
11.             Container contentPane = frame.getContentPane();  
12.             SpringLayout layout = new SpringLayout();  
13.             contentPane.setLayout(layout);  
14.   
15.             JLabel label = new JLabel("Label: ");  
16.             JTextField textField = new JTextField("My Text Field", 15);  
17.             contentPane.add(label);  
18.             contentPane.add(textField);  
19.        
20.             layout.putConstraint(SpringLayout.WEST, label,6,SpringLayout.WEST, contentPane);  
21.             layout.putConstraint(SpringLayout.NORTH, label,6,SpringLayout.NORTH, contentPane);  
22.             layout.putConstraint(SpringLayout.WEST, textField,6,SpringLayout.EAST, label);  
23.             layout.putConstraint(SpringLayout.NORTH, textField,6,SpringLayout.NORTH, contentPane);  
24.             layout.putConstraint(SpringLayout.EAST, contentPane,6,SpringLayout.EAST, textField);  
25.             layout.putConstraint(SpringLayout.SOUTH, contentPane,6,SpringLayout.SOUTH, textField);  
26.   
27.             frame.pack();  
28.             frame.setVisible(true);  
29.         }  
30.         public static void main(String[] args) {  
31.             javax.swing.SwingUtilities.invokeLater(new Runnable() {  
32.                 public void run() {  
33.                     createAndShowGUI();  
34.                 }  
35.             });  
36.         }  
37.     }  

Output:

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GroupLayout in java ~ java help

GroupLayout groups its components and places them in a Container hierarchically. The grouping is done by instances of the Group class.

Group is an abstract class and two concrete classes which implement this Group class are SequentialGroup and ParallelGroup.

SequentialGroup positions its child sequentially one after another where as ParallelGroup aligns its child on top of each other.

The GroupLayout class provides methods such as createParallelGroup() and createSequentialGroup() to create groups.

GroupLayout treats each axis independently. That is, there is a group representing the horizontal axis, and a group representing the vertical axis. Each component must exists in both a horizontal and vertical group, otherwise an IllegalStateException is thrown during layout, or when the minimum, preferred or maximum size is requested.

Nested Classes

Modifier and Type	Class	Description
static class	GroupLayout.Alignment	Enumeration of the possible ways ParallelGroup can align its children.
class	GroupLayout.Group	Group provides the basis for the two types of operations supported by GroupLayout: laying out components one after another (SequentialGroup) or aligned (ParallelGroup).
class	GroupLayout.ParallelGroup	It is a Group that aligns and sizes it's children.
class	GroupLayout.SequentialGroup	It is a Group that positions and sizes its elements sequentially, one after another.

Fields

Modifier and Type	Field	Description
static int	DEFAULT_SIZE	It indicates the size from the component or gap should be used for a particular range value.
static int	PREFERRED_SIZE	It indicates the preferred size from the component or gap should be used for a particular range value.

Constructors

GroupLayout(Container host)

It creates a GroupLayout for the specified Container.

Useful Methods

Modifier and Type	Field	Description
void	addLayoutComponent(Component component, Object constraints)	It notify that a Component has been added to the parent container.
void	addLayoutComponent(String name, Component component)	It notify that a Component has been added to the parent container.
GroupLayout.ParallelGroup	createBaselineGroup(boolean resizable, boolean anchorBaselineToTop)	It creates and returns a ParallelGroup that aligns it's elements along the baseline.
GroupLayout.ParallelGroup	createParallelGroup()	It creates and returns a ParallelGroup with an alignment of Alignment.LEADING
GroupLayout.ParallelGroup	createParallelGroup(GroupLayout.Alignment alignment)	It creates and returns a ParallelGroup with the specified alignment.
GroupLayout.ParallelGroup	createParallelGroup(GroupLayout.Alignment alignment, boolean resizable)	It creates and returns a ParallelGroup with the specified alignment and resize behavior.
GroupLayout.SequentialGroup	createSequentialGroup()	It creates and returns a SequentialGroup.
boolean	getAutoCreateContainerGaps()	It returns true if gaps between the container and components that border the container are automatically created.
boolean	getAutoCreateGaps()	It returns true if gaps between components are automatically created.
boolean	getHonorsVisibility()	It returns whether component visiblity is considered when sizing and positioning components.
float	getLayoutAlignmentX(Container parent)	It returns the alignment along the x axis.
float	getLayoutAlignmentY(Container parent)	It returns the alignment along the y axis.
Dimension	maximumLayoutSize(Container parent)	It returns the maximum size for the specified container.

Example

1. public class GroupExample {  
2.     public static void main(String[] args) {  
3.         JFrame frame = new JFrame("GroupLayoutExample");  
4.         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
5.         Container contentPanel = frame.getContentPane();  
6.         GroupLayout groupLayout = new GroupLayout(contentPanel);  
7.   
8.         contentPanel.setLayout(groupLayout);  
9.   
10.         JLabel clickMe = new JLabel("Click Here");  
11.         JButton button = new JButton("This Button");  
12.   
13.         groupLayout.setHorizontalGroup(  
14.                     groupLayout.createSequentialGroup()  
15.                                 .addComponent(clickMe)  
16.                                 .addGap(10, 20, 100)  
17.                                 .addComponent(button));  
18.         groupLayout.setVerticalGroup(  
19.                      groupLayout.createParallelGroup(GroupLayout.Alignment.BASELINE)  
20.                                 .addComponent(clickMe)  
21.                                 .addComponent(button));  
22.         frame.pack();  
23.         frame.setVisible(true);  
24.     }  
25. }  

Output:

Example 2

1. import java.awt.Container;  
2. import javax.swing.GroupLayout;  
3. import javax.swing.JButton;  
4. import javax.swing.JFrame;  
5. import static javax.swing.GroupLayout.Alignment.*;  
6. public class GroupExample2 {  
7.     public static void main(String[] args) {  
8.         JFrame frame = new JFrame("GroupLayoutExample");  
9.         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
10.         Container myPanel = frame.getContentPane();  
11.   
12.         GroupLayout groupLayout = new GroupLayout(myPanel);  
13.         groupLayout.setAutoCreateGaps(true);  
14.         groupLayout.setAutoCreateContainerGaps(true);  
15.         myPanel.setLayout(groupLayout);  
16.   
17.         JButton b1 = new JButton("Button One");  
18.         JButton b2 = new JButton("Button Two");  
19.         JButton b3 = new JButton("Button Three");  
20.   
21.         groupLayout.setHorizontalGroup(groupLayout.createSequentialGroup()  
22.                 .addGroup(groupLayout.createParallelGroup(LEADING).addComponent(b1).addComponent(b3))  
23.                 .addGroup(groupLayout.createParallelGroup(TRAILING).addComponent(b2)));  
24.   
25.         groupLayout.setVerticalGroup(groupLayout.createSequentialGroup()  
26.                 .addGroup(groupLayout.createParallelGroup(BASELINE).addComponent(b1).addComponent(b2))  
27.                 .addGroup(groupLayout.createParallelGroup(BASELINE).addComponent(b3)));  
28.   
29.         frame.pack();  
30.         frame.setVisible(true);  
31.     }  
32. }  

Output:

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