SpringLayout
Class SpringLayout
- java.lang.Object
-
- javax.swing.SpringLayout
- All Implemented Interfaces:
- LayoutManager, LayoutManager2
public class SpringLayout extends Object implements LayoutManager2
A 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 uses SpringLayout, 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 Classes
Modifier and Type | Class and Description |
---|---|
static class |
SpringLayout.Constraints A |
Fields
NORTH
public static final String NORTH
Specifies the top edge of a component's bounding rectangle.
SOUTH
public static final String SOUTH
Specifies the bottom edge of a component's bounding rectangle.
EAST
public static final String EAST
Specifies the right edge of a component's bounding rectangle.
WEST
public static final String WEST
Specifies the left edge of a component's bounding rectangle.
HORIZONTAL_CENTER
public static final String HORIZONTAL_CENTER
Specifies the horizontal center of a component's bounding rectangle.
- Since:
- 1.6
VERTICAL_CENTER
public static final String VERTICAL_CENTER
Specifies the vertical center of a component's bounding rectangle.
- Since:
- 1.6
BASELINE
public static final String BASELINE
Specifies the baseline of a component.
- Since:
- 1.6
WIDTH
public static final String WIDTH
Specifies the width of a component's bounding rectangle.
- Since:
- 1.6
HEIGHT
public static final String HEIGHT
Specifies the height of a component's bounding rectangle.
- Since:
- 1.6
Constructors
SpringLayout
public SpringLayout()
Constructs a new SpringLayout
.
Methods
addLayoutComponent
public void addLayoutComponent(String name, Component c)
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 component -
c
- the component to be added
removeLayoutComponent
public void removeLayoutComponent(Component c)
Removes the constraints associated with the specified component.
- Specified by:
-
removeLayoutComponent
in interfaceLayoutManager
- Parameters:
-
c
- the component being removed from the container
minimumLayoutSize
public Dimension minimumLayoutSize(Container parent)
Description copied from interface: LayoutManager
Calculates the minimum size dimensions for the specified container, given the components it contains.
- Specified by:
-
minimumLayoutSize
in interfaceLayoutManager
- Parameters:
-
parent
- the component to be laid out - See Also:
LayoutManager.preferredLayoutSize(java.awt.Container)
preferredLayoutSize
public Dimension preferredLayoutSize(Container parent)
Description copied from interface: LayoutManager
Calculates the preferred size dimensions for the specified container, given the components it contains.
- Specified by:
-
preferredLayoutSize
in interfaceLayoutManager
- Parameters:
-
parent
- the container to be laid out - See Also:
LayoutManager.minimumLayoutSize(java.awt.Container)
maximumLayoutSize
public Dimension maximumLayoutSize(Container parent)
Description copied from interface: LayoutManager2
Calculates the maximum size dimensions for the specified container, given the components it contains.
- Specified by:
-
maximumLayoutSize
in interfaceLayoutManager2
- See Also:
-
Component.getMaximumSize()
,LayoutManager
addLayoutComponent
public void addLayoutComponent(Component component, Object constraints)
If constraints
is an instance of SpringLayout.Constraints
, associates the constraints with the specified component.
- Specified by:
-
addLayoutComponent
in interfaceLayoutManager2
- Parameters:
-
component
- the component being added -
constraints
- the component's constraints - See Also:
SpringLayout.Constraints
getLayoutAlignmentX
public float getLayoutAlignmentX(Container p)
Returns 0.5f (centered).
- Specified by:
-
getLayoutAlignmentX
in interfaceLayoutManager2
getLayoutAlignmentY
public float getLayoutAlignmentY(Container p)
Returns 0.5f (centered).
- Specified by:
-
getLayoutAlignmentY
in interfaceLayoutManager2
invalidateLayout
public void invalidateLayout(Container p)
Description copied from interface: LayoutManager2
Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.
- Specified by:
-
invalidateLayout
in interfaceLayoutManager2
putConstraint
public void putConstraint(String e1, Component c1, int pad, String e2, Component c2)
Links edge e1
of component c1
to edge e2
of component c2
, with a fixed distance between the edges. This constraint will cause the assignment
value(e1, c1) = value(e2, c2) + padto take place during all subsequent layout operations.
- Parameters:
-
e1
- the edge of the dependent -
c1
- the component of the dependent -
pad
- the fixed distance between dependent and anchor -
e2
- the edge of the anchor -
c2
- the component of the anchor - See Also:
putConstraint(String, Component, Spring, String, Component)
putConstraint
public void putConstraint(String e1, Component c1, Spring s, String e2, Component c2)
Links edge e1
of component c1
to edge e2
of component c2
. As edge (e2, c2)
changes value, edge (e1, c1)
will be calculated by taking the (spring) sum of (e2, c2)
and s
. Each edge must have one of the following values: SpringLayout.NORTH
, SpringLayout.SOUTH
, SpringLayout.EAST
, SpringLayout.WEST
, SpringLayout.VERTICAL_CENTER
, SpringLayout.HORIZONTAL_CENTER
or SpringLayout.BASELINE
.
- Parameters:
-
e1
- the edge of the dependent -
c1
- the component of the dependent -
s
- the spring linking dependent and anchor -
e2
- the edge of the anchor -
c2
- the component of the anchor - See Also:
-
putConstraint(String, Component, int, String, Component)
,NORTH
,SOUTH
,EAST
,WEST
,VERTICAL_CENTER
,HORIZONTAL_CENTER
,BASELINE
getConstraints
public SpringLayout.Constraints getConstraints(Component c)
Returns the constraints for the specified component. Note that, unlike the GridBagLayout
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
public 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. 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 by SpringLayout
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
layoutContainer
public void layoutContainer(Container parent)
Description copied from interface: LayoutManager
Lays out the specified container.
- Specified by:
-
layoutContainer
in interfaceLayoutManager
- Parameters:
-
parent
- the container to be laid out
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