Module java.desktop
Package javax.swing

# 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 Class Summary

Nested Classes
Modifier and Type
Class
Description
`static class`
`SpringLayout.Constraints`
A `Constraints` object holds the constraints that govern the way a component's size and position change in a container controlled by a `SpringLayout`.

## Field Summary

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

## Constructor Summary

Constructors
Constructor
Description
`SpringLayout()`
Constructs a new `SpringLayout`.

## Method Summary

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)`
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`
`invalidateLayout(Container p)`
Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.
`void`
`layoutContainer(Container parent)`
Lays out the specified container.
`Dimension`
`maximumLayoutSize(Container parent)`
Calculates the maximum size dimensions for the specified container, given the components it contains.
`Dimension`
`minimumLayoutSize(Container parent)`
Calculates the minimum size dimensions for the specified container, given the components it contains.
`Dimension`
`preferredLayoutSize(Container parent)`
Calculates the preferred size dimensions for the specified container, given the components it contains.
`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.
`void`
`putConstraint(String e1, Component c1, Spring s, String e2, Component c2)`
Links edge `e1` of component `c1` to edge `e2` of component `c2`.
`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`

## Field Details

### NORTH

public static final String NORTH
Specifies the top edge of a component's bounding rectangle.

See Also:
  - Constant Field Values

### SOUTH

public static final String SOUTH
Specifies the bottom edge of a component's bounding rectangle.

See Also:
  - Constant Field Values

### EAST

public static final String EAST
Specifies the right edge of a component's bounding rectangle.

See Also:
  - Constant Field Values

### WEST

public static final String WEST
Specifies the left edge of a component's bounding rectangle.

See Also:
  - Constant Field Values

### HORIZONTAL_CENTER

public static final String HORIZONTAL_CENTER
Specifies the horizontal center of a component's bounding rectangle.

Since:
  1.6
See Also:
  - Constant Field Values

### VERTICAL_CENTER

public static final String VERTICAL_CENTER
Specifies the vertical center of a component's bounding rectangle.

Since:
  1.6
See Also:
  - Constant Field Values

### BASELINE

public static final String BASELINE
Specifies the baseline of a component.

Since:
  1.6
See Also:
  - Constant Field Values

### WIDTH

public static final String WIDTH
Specifies the width of a component's bounding rectangle.

Since:
  1.6
See Also:
  - Constant Field Values

### HEIGHT

public static final String 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 new `SpringLayout`.

## Method Details

### 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 interface `LayoutManager`
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 interface `LayoutManager`
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 interface `LayoutManager`
Parameters:
  `parent` - the component to be laid out
Returns:
  the minimum dimension for the container
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 interface `LayoutManager`
Parameters:
  `parent` - the container to be laid out
Returns:
  the preferred dimension for the container
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 interface `LayoutManager2`
Parameters:
  `parent` - the target container
Returns:
  the maximum size of the container
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 interface `LayoutManager2`
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 interface `LayoutManager2`
Parameters:
  `p` - the target container
Returns:
  the x-axis alignment preference

### getLayoutAlignmentY

public float getLayoutAlignmentY(Container p)
Returns 0.5f (centered).

Specified by:
  `getLayoutAlignmentY` in interface `LayoutManager2`
Parameters:
  `p` - the target container
Returns:
  the y-axis alignment preference

### 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 interface `LayoutManager2`
Parameters:
  `p` - the target container

### 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) + pad

to 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 of `SpringLayout.NORTH`, `SpringLayout.SOUTH`, `SpringLayout.EAST`, `SpringLayout.WEST`, `SpringLayout.VERTICAL_CENTER`, `SpringLayout.HORIZONTAL_CENTER` or `SpringLayout.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 interface `LayoutManager`
Parameters:
  `parent` - the container to be laid out