- All Implemented Interfaces:
LayoutManager
,LayoutManager2
public class SpringLayout extends Object implements LayoutManager2
SpringLayout
lays out the children of its associated container
according to a set of constraints.
See How to Use SpringLayout
in The Java Tutorial for examples of using
SpringLayout
.
Each constraint,
represented by a Spring
object,
controls the vertical or horizontal distance
between two component edges.
The edges can belong to
any child of the container,
or to the container itself.
For example,
the allowable width of a component
can be expressed using a constraint
that controls the distance between the west (left) and east (right)
edges of the component.
The allowable y coordinates for a component
can be expressed by constraining the distance between
the north (top) edge of the component
and the north edge of its container.
Every child of a SpringLayout
-controlled container,
as well as the container itself,
has exactly one set of constraints
associated with it.
These constraints are represented by
a SpringLayout.Constraints
object.
By default,
SpringLayout
creates constraints
that make their associated component
have the minimum, preferred, and maximum sizes
returned by the component's
Component.getMinimumSize()
,
Component.getPreferredSize()
, and
Component.getMaximumSize()
methods. The x and y positions are initially not
constrained, so that until you constrain them the Component
will be positioned at 0,0 relative to the Insets
of the
parent Container
.
You can change
a component's constraints in several ways.
You can
use one of the
putConstraint
methods
to establish a spring
linking the edges of two components within the same container.
Or you can get the appropriate SpringLayout.Constraints
object using
getConstraints
and then modify one or more of its springs.
Or you can get the spring for a particular edge of a component
using getConstraint
,
and modify it.
You can also associate
your own SpringLayout.Constraints
object
with a component by specifying the constraints object
when you add the component to its container
(using
Container.add(Component, Object)
).
The Spring
object representing each constraint
has a minimum, preferred, maximum, and current value.
The current value of the spring
is somewhere between the minimum and maximum values,
according to the formula given in the
Spring.sum(javax.swing.Spring, javax.swing.Spring)
method description.
When the minimum, preferred, and maximum values are the same,
the current value is always equal to them;
this inflexible spring is called a strut.
You can create struts using the factory method
Spring.constant(int)
.
The Spring
class also provides factory methods
for creating other kinds of springs,
including springs that depend on other springs.
In a SpringLayout
, the position of each edge is dependent on
the position of just one other edge. If a constraint is subsequently added
to create a new binding for an edge, the previous binding is discarded
and the edge remains dependent on a single edge.
Springs should only be attached
between edges of the container and its immediate children; the behavior
of the SpringLayout
when presented with constraints linking
the edges of components from different containers (either internal or
external) is undefined.
SpringLayout vs. Other Layout Managers
Note: Unlike many layout managers,SpringLayout
doesn't automatically set the location of the components it manages. If you hand-code a GUI that usesSpringLayout
, remember to initialize component locations by constraining the west/east and north/south locations.Depending on the constraints you use, you may also need to set the size of the container explicitly.
Despite the simplicity of SpringLayout
,
it can emulate the behavior of most other layout managers.
For some features,
such as the line breaking provided by FlowLayout
,
you'll need to
create a special-purpose subclass of the Spring
class.
SpringLayout
also provides a way to solve
many of the difficult layout
problems that cannot be solved by nesting combinations
of Box
es. That said, SpringLayout
honors the
LayoutManager2
contract correctly and so can be nested with
other layout managers -- a technique that can be preferable to
creating the constraints implied by the other layout managers.
The asymptotic complexity of the layout operation of a SpringLayout
is linear in the number of constraints (and/or components).
Warning:
Serialized objects of this class will not be compatible with
future Swing releases. The current serialization support is
appropriate for short term storage or RMI between applications running
the same version of Swing. As of 1.4, support for long term storage
of all JavaBeans
has been added to the java.beans
package.
Please see XMLEncoder
.
- Since:
- 1.4
- See Also:
Spring
,SpringLayout.Constraints
-
Nested Class Summary
Nested Classes Modifier and Type Class Description static class
SpringLayout.Constraints
AConstraints
object holds the constraints that govern the way a component's size and position change in a container controlled by aSpringLayout
. -
Field Summary
Fields Modifier and Type Field Description static String
BASELINE
Specifies the baseline of a component.static String
EAST
Specifies the right edge of a component's bounding rectangle.static String
HEIGHT
Specifies the height of a component's bounding rectangle.static String
HORIZONTAL_CENTER
Specifies the horizontal center of a component's bounding rectangle.static String
NORTH
Specifies the top edge of a component's bounding rectangle.static String
SOUTH
Specifies the bottom edge of a component's bounding rectangle.static String
VERTICAL_CENTER
Specifies the vertical center of a component's bounding rectangle.static String
WEST
Specifies the left edge of a component's bounding rectangle.static String
WIDTH
Specifies the width of a component's bounding rectangle. -
Constructor Summary
Constructors Constructor Description SpringLayout()
Constructs a newSpringLayout
. -
Method Summary
Modifier and Type Method Description void
addLayoutComponent(Component component, Object constraints)
Ifconstraints
is an instance ofSpringLayout.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)
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)
Returns the constraints for the specified component.float
getLayoutAlignmentX(Container p)
Returns 0.5f (centered).float
getLayoutAlignmentY(Container p)
Returns 0.5f (centered).void
putConstraint(String e1, Component c1, int pad, String e2, Component c2)
Links edgee1
of componentc1
to edgee2
of componentc2
, with a fixed distance between the edges.void
putConstraint(String e1, Component c1, Spring s, String e2, Component c2)
Links edgee1
of componentc1
to edgee2
of componentc2
.void
removeLayoutComponent(Component c)
Removes the constraints associated with the specified component.Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
Methods declared in interface java.awt.LayoutManager
layoutContainer, minimumLayoutSize, preferredLayoutSize
Methods declared in interface java.awt.LayoutManager2
invalidateLayout, maximumLayoutSize
-
Field Details
-
NORTH
Specifies the top edge of a component's bounding rectangle.- See Also:
- Constant Field Values
-
SOUTH
Specifies the bottom edge of a component's bounding rectangle.- See Also:
- Constant Field Values
-
EAST
Specifies the right edge of a component's bounding rectangle.- See Also:
- Constant Field Values
-
WEST
Specifies the left edge of a component's bounding rectangle.- See Also:
- Constant Field Values
-
HORIZONTAL_CENTER
Specifies the horizontal center of a component's bounding rectangle.- Since:
- 1.6
- See Also:
- Constant Field Values
-
VERTICAL_CENTER
Specifies the vertical center of a component's bounding rectangle.- Since:
- 1.6
- See Also:
- Constant Field Values
-
BASELINE
Specifies the baseline of a component.- Since:
- 1.6
- See Also:
- Constant Field Values
-
WIDTH
Specifies the width of a component's bounding rectangle.- Since:
- 1.6
- See Also:
- Constant Field Values
-
HEIGHT
Specifies the height of a component's bounding rectangle.- Since:
- 1.6
- See Also:
- Constant Field Values
-
-
Constructor Details
-
SpringLayout
public SpringLayout()Constructs a newSpringLayout
.
-
-
Method Details
-
addLayoutComponent
Has no effect, since this layout manager does not use a per-component string.- Specified by:
addLayoutComponent
in interfaceLayoutManager
- Parameters:
name
- the string to be associated with the componentc
- the component to be added
-
removeLayoutComponent
Removes the constraints associated with the specified component.- Specified by:
removeLayoutComponent
in interfaceLayoutManager
- Parameters:
c
- the component being removed from the container
-
addLayoutComponent
Ifconstraints
is an instance ofSpringLayout.Constraints
, associates the constraints with the specified component.- Specified by:
addLayoutComponent
in interfaceLayoutManager2
- Parameters:
component
- the component being addedconstraints
- the component's constraints- See Also:
SpringLayout.Constraints
-
getLayoutAlignmentX
Returns 0.5f (centered).- Specified by:
getLayoutAlignmentX
in interfaceLayoutManager2
- Parameters:
p
- the target container- Returns:
- the x-axis alignment preference
-
getLayoutAlignmentY
Returns 0.5f (centered).- Specified by:
getLayoutAlignmentY
in interfaceLayoutManager2
- Parameters:
p
- the target container- Returns:
- the y-axis alignment preference
-
putConstraint
Links edgee1
of componentc1
to edgee2
of componentc2
, with a fixed distance between the edges. This constraint will cause the assignmentvalue(e1, c1) = value(e2, c2) + pad
to take place during all subsequent layout operations.- Parameters:
e1
- the edge of the dependentc1
- the component of the dependentpad
- the fixed distance between dependent and anchore2
- the edge of the anchorc2
- the component of the anchor- See Also:
putConstraint(String, Component, Spring, String, Component)
-
putConstraint
Links edgee1
of componentc1
to edgee2
of componentc2
. As edge(e2, c2)
changes value, edge(e1, c1)
will be calculated by taking the (spring) sum of(e2, c2)
ands
. Each edge must have one of the following values:SpringLayout.NORTH
,SpringLayout.SOUTH
,SpringLayout.EAST
,SpringLayout.WEST
,SpringLayout.VERTICAL_CENTER
,SpringLayout.HORIZONTAL_CENTER
orSpringLayout.BASELINE
.- Parameters:
e1
- the edge of the dependentc1
- the component of the dependents
- the spring linking dependent and anchore2
- the edge of the anchorc2
- the component of the anchor- See Also:
putConstraint(String, Component, int, String, Component)
,NORTH
,SOUTH
,EAST
,WEST
,VERTICAL_CENTER
,HORIZONTAL_CENTER
,BASELINE
-
getConstraints
Returns the constraints for the specified component. Note that, unlike theGridBagLayout
getConstraints
method, this method does not clone constraints. If no constraints have been associated with this component, this method returns a default constraints object positioned at 0,0 relative to the parent's Insets and its width/height constrained to the minimum, maximum, and preferred sizes of the component. The size characteristics are not frozen at the time this method is called; instead this method returns a constraints object whose characteristics track the characteristics of the component as they change.- Parameters:
c
- the component whose constraints will be returned- Returns:
- the constraints for the specified component
-
getConstraint
Returns the spring controlling the distance between the specified edge of the component and the top or left edge of its parent. This method, instead of returning the current binding for the edge, returns a proxy that tracks the characteristics of the edge even if the edge is subsequently rebound. Proxies are intended to be used in builder environments where it is useful to allow the user to define the constraints for a layout in any order. Proxies do, however, provide the means to create cyclic dependencies amongst the constraints of a layout. Such cycles are detected internally bySpringLayout
so that the layout operation always terminates.- Parameters:
edgeName
- must be one ofSpringLayout.NORTH
,SpringLayout.SOUTH
,SpringLayout.EAST
,SpringLayout.WEST
,SpringLayout.VERTICAL_CENTER
,SpringLayout.HORIZONTAL_CENTER
orSpringLayout.BASELINE
c
- the component whose edge spring is desired- Returns:
- a proxy for the spring controlling the distance between the specified edge and the top or left edge of its parent
- See Also:
NORTH
,SOUTH
,EAST
,WEST
,VERTICAL_CENTER
,HORIZONTAL_CENTER
,BASELINE
-