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 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 JavaBeans™ has been added to the java.beans package. Please see XMLEncoder.

Since:
1.4
See Also:
Spring, SpringLayout.Constraints

  • Field Details

  • 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

    • 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

    • 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