Module java.desktop
Package javax.swing

Class SpringLayout.Constraints

  • Enclosing class:
    SpringLayout
    public static class SpringLayout.Constraints
extends Object
    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 (here WEST and x are synonyms, as are and NORTH and y): 

                   EAST = WEST + WIDTH
              SOUTH = NORTH + HEIGHT
  HORIZONTAL_CENTER = WEST + WIDTH/2
    VERTICAL_CENTER = NORTH + HEIGHT/2
  ABSOLUTE_BASELINE = NORTH + RELATIVE_BASELINE*

    For example, if you have specified the WIDTH and WEST (X) location the EAST is calculated as WEST + WIDTH. If you instead specified the WIDTH and EAST locations the WEST (X) location is then calculated as EAST - WIDTH.

    [RELATIVE_BASELINE is a private constraint that is set automatically when the SpringLayout.Constraints(Component) constructor is called or when a constraints object is registered with a SpringLayout object.]

    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 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, a Constraints object can become over-constrained. For example, if the WEST, WIDTH and EAST edges are all set, steps must be taken to ensure that the first of the formulas above holds. To do this, the Constraints object throws away the least recently set constraint so as to make the formulas hold.

    Since:
    1.4

    • Constructor Detail

      • Constraints

        public Constraints()
        Creates an empty Constraints object.

      • Constraints

        public Constraints​(Spring x,
                   Spring y)
        Creates a Constraints object with the specified values for its x and y properties. The height and width springs have null values.
        Parameters:
        x - the spring controlling the component's x value
        y - the spring controlling the component's y value

      • Constraints

        public Constraints​(Spring x,
                   Spring y,
                   Spring width,
                   Spring height)
        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.
        Parameters:
        x - the spring value for the x property
        y - the spring value for the y property
        width - the spring value for the width property
        height - the spring value for the height property

      • Constraints

        public Constraints​(Component c)
        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.
        Parameters:
        c - the component whose characteristics will be reflected by this Constraints object
        Throws:
        NullPointerException - if c is null.
        Since:
        1.5