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
* {@link java.awt.Component#getMinimumSize},
* {@link java.awt.Component#getPreferredSize}, and
* {@link java.awt.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
* {@link #putConstraint 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
* {@link #getConstraints getConstraints}
* and then modify one or more of its springs.
* Or you can get the spring for a particular edge of a component
* using {@link #getConstraint 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
* {@link 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
* {@link Spring#sum} 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
* {@link 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.
*
*
** *
* Note: * Unlike many layout managers, *SpringLayoutdoesn'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 Boxes. 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 JavaBeansTM
* has been added to the java.beans package.
* Please see {@link java.beans.XMLEncoder}.
*
* @see Spring
* @see SpringLayout.Constraints
*
* @version 1.19 12/19/03
* @author Philip Milne
* @author Joe Winchester
* @since 1.4
*/
public class SpringLayout implements LayoutManager2 {
private Map componentConstraints = new HashMap();
private Spring cyclicReference = Spring.constant(Spring.UNSET);
private Set cyclicSprings;
private Set acyclicSprings;
/**
* Specifies the top edge of a component's bounding rectangle.
*/
public static final String NORTH = "North";
/**
* Specifies the bottom edge of a component's bounding rectangle.
*/
public static final String SOUTH = "South";
/**
* Specifies the right edge of a component's bounding rectangle.
*/
public static final String EAST = "East";
/**
* Specifies the left edge of a component's bounding rectangle.
*/
public static final String WEST = "West";
/**
* A Constraints object holds the
* constraints that govern the way a component's size and position
* change in a container controlled by a SpringLayout.
* A Constraints object is
* like a Rectangle, in that it
* has x, y,
* width, and height properties.
* In the Constraints object, however,
* these properties have
* Spring values instead of integers.
* In addition,
* a Constraints object
* can be manipulated as four edges
* -- north, south, east, and west --
* using the constraint property.
*
*
* The following formulas are always true
* for a Constraints object:
*
*
* west = x
* north = y
* east = x + width
* south = y + height
*
* Note: In this document,
* operators represent methods
* in the Spring class.
* For example, "a + b" is equal to
* Spring.sum(a, b),
* and "a - b" is equal to
* Spring.sum(a, Spring.minus(b)).
* See the
* {@link Spring Spring API documentation}
* for further details
* of spring arithmetic.
*
*
*
* Because a Constraints object's properties --
* representing its edges, size, and location -- can all be set
* independently and yet are interrelated,
* the object can become over-constrained.
* For example,
* if both the x and width
* properties are set
* and then the east edge is set,
* the object is over-constrained horizontally.
* When this happens, one of the values
* (in this case, the x property)
* automatically changes so
* that the formulas still hold.
*
*
* The following table shows which value changes
* when a Constraints object
* is over-constrained horizontally.
*
*
*
*
*
* Value Being Set
(method used)
* Result When Over-Constrained Horizontally
* (x, width, and the east edge are all non-null)
*
*
* x or the west edge
(setX or setConstraint)width value is automatically set to east - x.
*
* width
(setWidth)east edge's value is automatically set to x + width.
*
*
* east edge
(setConstraint)
* x value is automatically set to east - width.
*
*
*
* The rules for the vertical properties are similar:
*
*
*
*
* Value Being Set
(method used)
* Result When Over-Constrained Vertically
(y, height, and the south edge are all non-null)
*
*
* y or the north edge
(setY or setConstraint)height value is automatically set to south - y.
*
* height
(setHeight)south edge's value is automatically set to y + height.
*
*
* south edge
(setConstraint)
* y value is automatically set to south - height.
*
*
*/
public static class Constraints {
private Spring x;
private Spring y;
private Spring width;
private Spring height;
private Spring east;
private Spring south;
private Spring verticalDerived = null;
private Spring horizontalDerived = null;
/**
* Creates an empty Constraints object.
*/
public Constraints() {
this(null, null, null, null);
}
/**
* Creates a Constraints object with the
* specified values for its
* x and y properties.
* The height and width springs
* have null values.
*
* @param x the spring controlling the component's x value
* @param y the spring controlling the component's y value
*/
public Constraints(Spring x, Spring y) {
this(x, y, null, null);
}
/**
* Creates a Constraints object with the
* specified values for its
* x, y, width,
* and height properties.
* Note: If the SpringLayout class
* encounters null values in the
* Constraints object of a given component,
* it replaces them with suitable defaults.
*
* @param x the spring value for the x property
* @param y the spring value for the y property
* @param width the spring value for the width property
* @param height the spring value for the height property
*/
public Constraints(Spring x, Spring y, Spring width, Spring height) {
this.x = x;
this.y = y;
this.width = width;
this.height = height;
}
/**
* Creates a Constraints object with
* suitable x, y, width and
* height springs for component, c.
* The x and y springs are constant
* springs initialised with the component's location at
* the time this method is called. The width and
* height springs are special springs, created by
* the Spring.width() and Spring.height()
* methods, which track the size characteristics of the component
* when they change.
*
* @param c the component whose characteristics will be reflected by this Constraints object
* @throws NullPointerException if c is null.
* @since 1.5
*/
public Constraints(Component c) {
this.x = Spring.constant(c.getX());
this.y = Spring.constant(c.getY());
this.width = Spring.width(c);
this.height = Spring.height(c);
}
private boolean overConstrainedHorizontally() {
return (x != null) && (width != null) && (east != null);
}
private boolean overConstrainedVertically() {
return (y != null) && (height != null) && (south != null);
}
private Spring sum(Spring s1, Spring s2) {
return (s1 == null || s2 == null) ? null : Spring.sum(s1, s2);
}
private Spring difference(Spring s1, Spring s2) {
return (s1 == null || s2 == null) ? null : Spring.difference(s1, s2);
}
/**
* Sets the x property,
* which controls the x value
* of a component's location.
*
* @param x the spring controlling the x value
* of a component's location
*
* @see #getX
* @see SpringLayout.Constraints
*/
public void setX(Spring x) {
this.x = x;
horizontalDerived = null;
if (overConstrainedHorizontally()) {
width = null;
}
}
/**
* Returns the value of the x property.
*
* @return the spring controlling the x value
* of a component's location
*
* @see #setX
* @see SpringLayout.Constraints
*/
public Spring getX() {
if (x != null) {
return x;
}
if (horizontalDerived == null) {
horizontalDerived = difference(east, width);
}
return horizontalDerived;
}
/**
* Sets the y property,
* which controls the y value
* of a component's location.
*
* @param y the spring controlling the y value
* of a component's location
*
* @see #getY
* @see SpringLayout.Constraints
*/
public void setY(Spring y) {
this.y = y;
verticalDerived = null;
if (overConstrainedVertically()) {
height = null;
}
}
/**
* Returns the value of the y property.
*
* @return the spring controlling the y value
* of a component's location
*
* @see #setY
* @see SpringLayout.Constraints
*/
public Spring getY() {
if (y != null) {
return y;
}
if (verticalDerived == null) {
verticalDerived = difference(south, height);
}
return verticalDerived;
}
/**
* Sets the width property,
* which controls the width of a component.
*
* @param width the spring controlling the width of this
* Constraints object
*
* @see #getWidth
* @see SpringLayout.Constraints
*/
public void setWidth(Spring width) {
this.width = width;
horizontalDerived = null;
if (overConstrainedHorizontally()) {
east = null;
}
}
/**
* Returns the value of the width property.
*
* @return the spring controlling the width of a component
*
* @see #setWidth
* @see SpringLayout.Constraints
*/
public Spring getWidth() {
if (width != null) {
return width;
}
if (horizontalDerived == null) {
horizontalDerived = difference(east, x);
}
return horizontalDerived;
}
/**
* Sets the height property,
* which controls the height of a component.
*
* @param height the spring controlling the height of this Constraints
* object
*
* @see #getHeight
* @see SpringLayout.Constraints
*/
public void setHeight(Spring height) {
this.height = height;
verticalDerived = null;
if (overConstrainedVertically()) {
south = null;
}
}
/**
* Returns the value of the height property.
*
* @return the spring controlling the height of a component
*
* @see #setHeight
* @see SpringLayout.Constraints
*/
public Spring getHeight() {
if (height != null) {
return height;
}
if (verticalDerived == null) {
verticalDerived = difference(south, y);
}
return verticalDerived;
}
private void setEast(Spring east) {
this.east = east;
horizontalDerived = null;
if (overConstrainedHorizontally()) {
x = null;
}
}
private Spring getEast() {
if (east != null) {
return east;
}
if (horizontalDerived == null) {
horizontalDerived = sum(x, width);
}
return horizontalDerived;
}
private void setSouth(Spring south) {
this.south = south;
verticalDerived = null;
if (overConstrainedVertically()) {
y = null;
}
}
private Spring getSouth() {
if (south != null) {
return south;
}
if (verticalDerived == null) {
verticalDerived = sum(y, height);
}
return verticalDerived;
}
/**
* Sets the spring controlling the specified edge.
* The edge must have one of the following values:
* SpringLayout.NORTH, SpringLayout.SOUTH,
* SpringLayout.EAST, SpringLayout.WEST.
*
* @param edgeName the edge to be set
* @param s the spring controlling the specified edge
*
* @see #getConstraint
* @see #NORTH
* @see #SOUTH
* @see #EAST
* @see #WEST
* @see SpringLayout.Constraints
*/
public void setConstraint(String edgeName, Spring s) {
edgeName = edgeName.intern();
if (edgeName == "West") {
setX(s);
}
else if (edgeName == "North") {
setY(s);
}
else if (edgeName == "East") {
setEast(s);
}
else if (edgeName == "South") {
setSouth(s);
}
}
/**
* Returns the value of the specified edge.
* The edge must have one of the following values:
* SpringLayout.NORTH, SpringLayout.SOUTH,
* SpringLayout.EAST, SpringLayout.WEST.
*
* @param edgeName the edge whose value
* is to be returned
*
* @return the spring controlling the specified edge
*
* @see #setConstraint
* @see #NORTH
* @see #SOUTH
* @see #EAST
* @see #WEST
* @see SpringLayout.Constraints
*/
public Spring getConstraint(String edgeName) {
edgeName = edgeName.intern();
return (edgeName == "West") ? getX() :
(edgeName == "North") ? getY() :
(edgeName == "East") ? getEast() :
(edgeName == "South") ? getSouth() :
null;
}
/*pp*/ void reset() {
if (x != null) x.setValue(Spring.UNSET);
if (y != null) y.setValue(Spring.UNSET);
if (width != null) width.setValue(Spring.UNSET);
if (height != null) height.setValue(Spring.UNSET);
if (east != null) east.setValue(Spring.UNSET);
if (south != null) south.setValue(Spring.UNSET);
if (horizontalDerived != null) horizontalDerived.setValue(Spring.UNSET);
if (verticalDerived != null) verticalDerived.setValue(Spring.UNSET);
}
}
private static class SpringProxy extends Spring {
private String edgeName;
private Component c;
private SpringLayout l;
public SpringProxy(String edgeName, Component c, SpringLayout l) {
this.edgeName = edgeName;
this.c = c;
this.l = l;
}
private Spring getConstraint() {
return l.getConstraints(c).getConstraint(edgeName);
}
public int getMinimumValue() {
return getConstraint().getMinimumValue();
}
public int getPreferredValue() {
return getConstraint().getPreferredValue();
}
public int getMaximumValue() {
return getConstraint().getMaximumValue();
}
public int getValue() {
return getConstraint().getValue();
}
public void setValue(int size) {
getConstraint().setValue(size);
}
/*pp*/ boolean isCyclic(SpringLayout l) {
return l.isCyclic(getConstraint());
}
public String toString() {
return "SpringProxy for " + edgeName + " edge of " + c.getName() + ".";
}
}
/**
* Constructs a new SpringLayout.
*/
public SpringLayout() {}
private void resetCyclicStatuses() {
cyclicSprings = new HashSet();
acyclicSprings = new HashSet();
}
private void setParent(Container p) {
resetCyclicStatuses();
Constraints pc = getConstraints(p);
pc.setX(Spring.constant(0));
pc.setY(Spring.constant(0));
// The applyDefaults() method automatically adds width and
// height springs that delegate their calculations to the
// getMinimumSize(), getPreferredSize() and getMaximumSize()
// methods of the relevant component. In the case of the
// parent this will cause an infinite loop since these
// methods, in turn, delegate their calculations to the
// layout manager. Check for this case and replace the
// the springs that would cause this problem with a
// constant springs that supply default values.
Spring width = pc.getWidth();
if (width instanceof Spring.WidthSpring && ((Spring.WidthSpring)width).c == p) {
pc.setWidth(Spring.constant(0, 0, Integer.MAX_VALUE));
}
Spring height = pc.getHeight();
if (height instanceof Spring.HeightSpring && ((Spring.HeightSpring)height).c == p) {
pc.setHeight(Spring.constant(0, 0, Integer.MAX_VALUE));
}
}
/*pp*/ boolean isCyclic(Spring s) {
if (s == null) {
return false;
}
if (cyclicSprings.contains(s)) {
return true;
}
if (acyclicSprings.contains(s)) {
return false;
}
cyclicSprings.add(s);
boolean result = s.isCyclic(this);
if (!result) {
acyclicSprings.add(s);
cyclicSprings.remove(s);
}
else {
System.err.println(s + " is cyclic. ");
}
return result;
}
private Spring abandonCycles(Spring s) {
return isCyclic(s) ? cyclicReference : s;
}
// LayoutManager methods.
/**
* Has no effect,
* since this layout manager does not
* use a per-component string.
*/
public void addLayoutComponent(String name, Component c) {}
/**
* Removes the constraints associated with the specified component.
*
* @param c the component being removed from the container
*/
public void removeLayoutComponent(Component c) {
componentConstraints.remove(c);
}
private static Dimension addInsets(int width, int height, Container p) {
Insets i = p.getInsets();
return new Dimension(width + i.left + i.right, height + i.top + i.bottom);
}
public Dimension minimumLayoutSize(Container parent) {
setParent(parent);
Constraints pc = getConstraints(parent);
return addInsets(abandonCycles(pc.getWidth()).getMinimumValue(),
abandonCycles(pc.getHeight()).getMinimumValue(),
parent);
}
public Dimension preferredLayoutSize(Container parent) {
setParent(parent);
Constraints pc = getConstraints(parent);
return addInsets(abandonCycles(pc.getWidth()).getPreferredValue(),
abandonCycles(pc.getHeight()).getPreferredValue(),
parent);
}
// LayoutManager2 methods.
public Dimension maximumLayoutSize(Container parent) {
setParent(parent);
Constraints pc = getConstraints(parent);
return addInsets(abandonCycles(pc.getWidth()).getMaximumValue(),
abandonCycles(pc.getHeight()).getMaximumValue(),
parent);
}
/**
* If constraints is an instance of
* SpringLayout.Constraints,
* associates the constraints with the specified component.
*
* @param component the component being added
* @param constraints the component's constraints
*
* @see SpringLayout.Constraints
*/
public void addLayoutComponent(Component component, Object constraints) {
if (constraints instanceof Constraints) {
putConstraints(component, (Constraints)constraints);
}
}
/**
* Returns 0.5f (centered).
*/
public float getLayoutAlignmentX(Container p) {
return 0.5f;
}
/**
* Returns 0.5f (centered).
*/
public float getLayoutAlignmentY(Container p) {
return 0.5f;
}
public void invalidateLayout(Container p) {}
// End of LayoutManger2 methods
/**
* 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.
*
* @param e1 the edge of the dependent
* @param c1 the component of the dependent
* @param pad the fixed distance between dependent and anchor
* @param e2 the edge of the anchor
* @param c2 the component of the anchor
*
* @see #putConstraint(String, Component, Spring, String, Component)
*/
public void putConstraint(String e1, Component c1, int pad, String e2, Component c2) {
putConstraint(e1, c1, Spring.constant(pad), e2, 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.
*
* @param e1 the edge of the dependent
* @param c1 the component of the dependent
* @param s the spring linking dependent and anchor
* @param e2 the edge of the anchor
* @param c2 the component of the anchor
*
* @see #putConstraint(String, Component, int, String, Component)
* @see #NORTH
* @see #SOUTH
* @see #EAST
* @see #WEST
*/
public void putConstraint(String e1, Component c1, Spring s, String e2, Component c2) {
putConstraint(e1, c1, Spring.sum(s, getConstraint(e2, c2)));
}
private void putConstraint(String e, Component c, Spring s) {
if (s != null) {
getConstraints(c).setConstraint(e, s);
}
}
private Constraints applyDefaults(Component c, Constraints constraints) {
if (constraints == null) {
constraints = new Constraints();
}
if (constraints.getWidth() == null) {
constraints.setWidth(new Spring.WidthSpring(c));
}
if (constraints.getHeight() == null) {
constraints.setHeight(new Spring.HeightSpring(c));
}
if (constraints.getX() == null) {
constraints.setX(Spring.constant(0));
}
if (constraints.getY() == null) {
constraints.setY(Spring.constant(0));
}
return constraints;
}
private void putConstraints(Component component, Constraints constraints) {
componentConstraints.put(component, applyDefaults(component, constraints));
}
/**
* 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.
*
* @param c the component whose constraints will be returned
*
* @return the constraints for the specified component
*/
public Constraints getConstraints(Component c) {
Constraints result = (Constraints)componentConstraints.get(c);
if (result == null) {
if (c instanceof javax.swing.JComponent) {
Object cp = ((javax.swing.JComponent)c).getClientProperty(SpringLayout.class);
if (cp instanceof Constraints) {
return applyDefaults(c, (Constraints)cp);
}
}
result = new Constraints();
putConstraints(c, result);
}
return result;
}
/**
* 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 envonments
* 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.
*
* @param edgeName must be
* SpringLayout.NORTH,
* SpringLayout.SOUTH,
* SpringLayout.EAST, or
* SpringLayout.WEST
* @param c the component whose edge spring is desired
*
* @return a proxy for the spring controlling the distance between the
* specified edge and the top or left edge of its parent
*
* @see #NORTH
* @see #SOUTH
* @see #EAST
* @see #WEST
*/
public Spring getConstraint(String edgeName, Component c) {
// The interning here is unnecessary; it was added for efficiency.
edgeName = edgeName.intern();
return new SpringProxy(edgeName, c, this);
}
public void layoutContainer(Container parent) {
setParent(parent);
int n = parent.getComponentCount();
getConstraints(parent).reset();
for (int i = 0 ; i < n ; i++) {
getConstraints(parent.getComponent(i)).reset();
}
Insets insets = parent.getInsets();
Constraints pc = getConstraints(parent);
abandonCycles(pc.getX()).setValue(0);
abandonCycles(pc.getY()).setValue(0);
abandonCycles(pc.getWidth()).setValue(parent.getWidth() -
insets.left - insets.right);
abandonCycles(pc.getHeight()).setValue(parent.getHeight() -
insets.top - insets.bottom);
for (int i = 0 ; i < n ; i++) {
Component c = parent.getComponent(i);
Constraints cc = getConstraints(c);
int x = abandonCycles(cc.getX()).getValue();
int y = abandonCycles(cc.getY()).getValue();
int width = abandonCycles(cc.getWidth()).getValue();
int height = abandonCycles(cc.getHeight()).getValue();
c.setBounds(insets.left + x, insets.top + y, width, height);
}
}
}