CS4812 Java for Jocks

1
CS4812 -- Java for Jocks

• Lecture 5 Components, Containers and Layout
  Managers

2
Review JDK 1.1 Events

• Last week, we say how the JDK 1.1 event model
  gives you three basic models to choose from
• Listener Interfaces
• Adapter Classes
• Semantic Events
• This week, we cover some basics on components,
  containers and layout--the business end of your
  event-driven GUI.

3
Layout Managers

• Defined LayoutManager is an interface specifying
  the following
• void addLayoutComponnet (String n, Component c)
• void removeLayoutComponent (String n, Comonent
  c)
• Dimension preferredLayoutSize (Container parent)
• Dimension minimumLayoutSize (Container parent)
• void layoutContainer (Container parent)

4
LayoutManager position and size

• Layout managers are used to calculate preferred
  and minimum sized for a container
• They also arrange component within the container
• Each container has associated with it exactly one
  layout manager
• But a single layout manager may do double duty,
  performing the layout for multiple containers

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A simple example . . .

• Public class MyPanel extends Container
• static LayoutManager fLayout new FlowLayout()
• . . .
• Public MyPanel()
• setLayout(fLayout())
• . . .

6
LayoutManagers Two General Flavors

• One can conceptually divide layout managers into
  two types
• those that attach constraints to their
  components, and . . .
• . . . those that do not
• What does this mean? If a manager attaches
  contraints to a component, information about a
  components location (e.g., compass points) is
  generated with the object.

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LayoutManagers Constraints

• BorderLayout specifies compass regions of a
  container

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LayoutManagers Constraints

• BorderLayouts then append constraint information
  on all components
• E.g.
• this.setLayout (new BorderLayout())
• Button e new Button (East)
• Button w new Button (West)
• add(e, East)
• add(w, West)

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LayoutManagers Constraints
10
LayoutManagers Another Example

• import java.awt.
• import java.applet.
• public class test extends Applet
• String Compass "North", "South", "East",
  "West", "Center"
• public void init()
• / ALWAYS call super init! /
• super.init()
• / set layout /
• setLayout(new BorderLayout())
• for (int iCompass.length i--gt0)
• add (new Button (Compassi),
  Compassi)

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LayoutManager Example

• Thus

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LayoutManager No Constraints

• The second type of LayoutManager does not specify
  constraints for the objects it holds.
• Examples
• GridLayout()
• FlowLayout()
• Without constraints, you cannot accurately
  predict layout behavior across platforms

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LayoutManager No Constraints

• Example FlowLayout
• import java.awt.
• import java.applet.
• public class test extends Applet
• public void init()
• super.init()
• String Labels "Short", "Short", "Long
  Label", "Really Long Label", "Really, really
  long"
• setLayout(new FlowLayout())
• for (int iLabels.length i--gt0)
• add (new Button (Labelsi))

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LayoutManager No Constraints

• Thus

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LayoutManager No Constraints

• And also

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LayoutManager No Constraints

• Note
• Since pixels, fonts and insets vary with each
  platform, layout without constraints will vary
  greatly.
• Lesson
• Use layout managers without constraints only when
  you have one or few components

17
LayoutManager No Constraints

• Do not suppose that layout manager without
  constraints are not useful!
• One of the most useful constraint-free layout
  manager is GridLayout.
• public GridLayout()
• public GridLayout(int rows, int cols)
• public GridLayout(int rows, int cols, int hgap,
  int vgap)

18
GridLayout Example

• import java.awt.
• import java.applet.
• public class test extends Applet
• public void init()
• super.init()
• setLayout(new GridLayout(4,3,5,5))
• int off-2,2,0
• for (int i10 i--gt1)
• add (new Button (""(ioffi3)))
• add (new Button ("."))
• add (new Button ("0"))
• add (new Button ("/-"))
• add (new MyPanel(null))

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GridLayout Example

• Thus

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Insets and LayoutManagers

• Layout management can be complemented by the use
  of Insets
• All containers have Insets--margins within which
  you may paint, but not position components
• unless a null layout is set!

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Insets--Did you know?

• When components are arranged in a container, Java
  calls the containers getInsets() accessor to
  determine margins.
• Insets vary with both the peer and the
  component--theres no way to know the default
  inset value!
• Insets for Frame objects are unusual in that they
  count the menubar (if any).
• Example
• public Insets getInsets()
• return new
• Insets(10,10,10,10)

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Using Insets

• Since components are not placed inside the
  insets, but you can nonetheless draw in the inset
  area, Insets are useful for adding graphic depth
  to layouts
• They can be used to add border, edging, and the
  like.
• Suppose we subclass panel to hold components, and
  specify an inset with colored edges . . .

23

• import java.awt.
• class MyPanel extends Panel
• int offset Component c
• public MyPanel () this (5, null)
• public MyPanel (Component c)this (5, c)
• public MyPanel(int offset, Component c)
• this.offset offset this.cc
• setLayout (new BorderLayout())
• if (c!null) add(c, "Center")
• public Insets getInsets()
• return new Insets(offset, offset, offset,
  offset)
• public void paint (Graphics g)
• Dimension D getSize() Insets I
  getInsets() if (c!null)
• g.setColor(Color.gray)
  g.fillRect(0,0,D.width, I.top)
  g.fillRect(0,0,I.left, D.height)
  g.fillRect(D.width-I.right, 0, I.right,
  D.height) g.fillRect(0,D.heigh
  t-I.bottom, D.width, D.height)else /WATCH
  THIS SPACE!/

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Example . . .

• Thus

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Introduction to Graphics Objects . . .

• Every component/container has associated with it
  a graphics object
• This graphics object can be use to draw on the
  component/container
• The graphics object is best accessed through the
  paint() method, which is automatically called by
  Java for updates
• You can also call paint() by requesting
  repaint() at key moments.

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Graphics and Insets

• While more specifics about graphics will come
  with the next lecture, we can use some basic
  graphics techniques to improve our panel class.
• Suppose we find a patter we wish to use as a
  background.
• Loading the pattern as an image can be costly in
  terms of time and memory.
• We could instead draw it ourselves . . .

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Graphics and Insets

• Find a pattern you like, and consider how you
  might duplicate it in the paint() method

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Graphics and Insets

• Our foregoing example breaks down to a few simple
  drawLine calls
• for (h0 hlt D.height h7)
• for (w0 wltD.width w7)
  g.drawLine(w,h, w4,h)
  g.drawLine(w4,h, w7,h3)
  g.drawLine(w7,h3,
  w7,h3)
  g.drawLine(w7,h3,w7,h5)
  g.drawLine(w7,h5,w6, h3)
  g.drawLine(w6,h3,
  w6,h6)
  g.drawLine(w6,h6,w6,h6)
  g.drawLine(w6,h6,w5,h3)
  g.drawLine(w5,h3,w1,h7)
  g.drawLine(w1,h7,w
  2,h7)
  g.drawLine(w,h4, w3,h1)
  g.drawLine(w3,h1,w1,h1)
  

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Graphics and insets . . .

• What would happen if we incorporated this pattern
  into our panel, and used null as a sort of
  switch to draw the pattern or the inset borders ?
  . . .

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• import java.awt.
• class MyPanel extends Panel
• int offset Component c
• public MyPanel () this (25, null)
• public MyPanel (Component c) this (5, c)
• public MyPanel(int offset, Component c)
• this.offset offset this.cc setLayout (new
  BorderLayout()) if (c!null) add(c, "Center")
• public Insets getInsets()
• return new Insets(offset, offset, offset,
  offset)
• public void paint (Graphics g)
• Dimension D getSize() Insets I getInsets()
• if (c!null)
• g.setColor(Color.gray)
• g.fillRect(0,0,D.width, I.top)
• g.fillRect(0,0,I.left, D.height)
• g.fillRect(D.width-I.right, 0, I.right,D.height)
• g.fillRect(0,D.height-I.bottom, D.width,
  D.height) else
• for (int h0 hlt D.height h7)
  for (int w0 wltD.width w7)
  
• g.drawLine(w,h, w4,h) g.drawLine(w4,h,
  w7,h3)

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• import java.awt.
• import java.applet.
• public class test extends Applet
• public void init()
• super.init()
• MyPanel m new MyPanel()
• m.setLayout(new GridLayout(4,3,5,5))
• int off-2,2,0 for (int i10 i--gt1) m.add
  (new MyPanel( (new Button (""(ioffi3)))))
• m.add (new MyPanel ( new Button ("."))) m.add
  (new MyPanel (new Button ("0")))
• m.add (new MyPanel (new Button ("/-")))
  add(m)
• public Insets getInsets()
• return new
• Insets(5,5,5,5)