Module java.desktop
Package javax.swing

# Class Spring

java.lang.Object
javax.swing.Spring

public abstract class Spring extends Object
An instance of the `Spring` class holds three properties that characterize its behavior: the minimum, preferred, and maximum values. Each of these properties may be involved in defining its fourth, value, property based on a series of rules.

An instance of the `Spring` class can be visualized as a mechanical spring that provides a corrective force as the spring is compressed or stretched away from its preferred value. This force is modelled as linear function of the distance from the preferred value, but with two different constants -- one for the compressional force and one for the tensional one. Those constants are specified by the minimum and maximum values of the spring such that a spring at its minimum value produces an equal and opposite force to that which is created when it is at its maximum value. The difference between the preferred and minimum values, therefore, represents the ease with which the spring can be compressed and the difference between its maximum and preferred values, indicates the ease with which the `Spring` can be extended. See the `sum(javax.swing.Spring, javax.swing.Spring)` method for details.

By defining simple arithmetic operations on `Spring`s, the behavior of a collection of `Spring`s can be reduced to that of an ordinary (non-compound) `Spring`. We define the "+", "-", max, and min operators on `Spring`s so that, in each case, the result is a `Spring` whose characteristics bear a useful mathematical relationship to its constituent springs.

A `Spring` can be treated as a pair of intervals with a single common point: the preferred value. The following rules define some of the arithmetic operators that can be applied to intervals (`[a, b]` refers to the interval from `a` to `b`, where `a <= b`).

              [a1, b1] + [a2, b2] = [a1 + a2, b1 + b2]

                          -[a, b] = [-b, -a]

          max([a1, b1], [a2, b2]) = [max(a1, a2), max(b1, b2)]

If we denote `Spring`s as `[a, b, c]`, where `a <= b <= c`, we can define the same arithmetic operators on `Spring`s:

              [a1, b1, c1] + [a2, b2, c2] = [a1 + a2, b1 + b2, c1 + c2]

                               -[a, b, c] = [-c, -b, -a]

          max([a1, b1, c1], [a2, b2, c2]) = [max(a1, a2), max(b1, b2), max(c1, c2)]

With both intervals and `Spring`s we can define "-" and min in terms of negation:

          X - Y = X + (-Y)

          min(X, Y) = -max(-X, -Y)

For the static methods in this class that embody the arithmetic operators, we do not actually perform the operation in question as that would snapshot the values of the properties of the method's arguments at the time the static method is called. Instead, the static methods create a new `Spring` instance containing references to the method's arguments so that the characteristics of the new spring track the potentially changing characteristics of the springs from which it was made. This is a little like the idea of a lazy value in a functional language.

If you are implementing a `SpringLayout` you can find further information and examples in How to Use SpringLayout, a section in The Java Tutorial.

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:
  - `SpringLayout`
  - `SpringLayout.Constraints`

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `static final int`
  `UNSET`
  An integer value signifying that a property value has not yet been calculated.

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `Spring()`
  Used by factory methods to create a `Spring`.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `static Spring`
  `constant(int pref)`
  Returns a strut -- a spring whose minimum, preferred, and maximum values each have the value `pref`.
  `static Spring`
  `constant(int min, int pref, int max)`
  Returns a spring whose minimum, preferred, and maximum values have the values: `min`, `pref`, and `max` respectively.
  `abstract int`
  `getMaximumValue()`
  Returns the maximum value of this `Spring`.
  `abstract int`
  `getMinimumValue()`
  Returns the minimum value of this `Spring`.
  `abstract int`
  `getPreferredValue()`
  Returns the preferred value of this `Spring`.
  `abstract int`
  `getValue()`
  Returns the current value of this `Spring`.
  `static Spring`
  `height(Component c)`
  Returns a spring whose minimum, preferred, maximum and value properties are defined by the heights of the minimumSize, preferredSize, maximumSize and size properties of the supplied component.
  `static Spring`
  `max(Spring s1, Spring s2)`
  Returns `max(s1, s2)`: a spring whose value is always greater than (or equal to) the values of both `s1` and `s2`.
  `static Spring`
  `minus(Spring s)`
  Returns `-s`: a spring running in the opposite direction to `s`.
  `static Spring`
  `scale(Spring s, float factor)`
  Returns a spring whose minimum, preferred, maximum and value properties are each multiples of the properties of the argument spring, `s`.
  `abstract void`
  `setValue(int value)`
  Sets the current value of this `Spring` to `value`.
  `static Spring`
  `sum(Spring s1, Spring s2)`
  Returns `s1+s2`: a spring representing `s1` and `s2` in series.
  `static Spring`
  `width(Component c)`
  Returns a spring whose minimum, preferred, maximum and value properties are defined by the widths of the minimumSize, preferredSize, maximumSize and size properties of the supplied component.

  ### Methods declared in class java.lang.Object

  `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- ## Field Details

  - ### UNSET

    public static final int UNSET
    An integer value signifying that a property value has not yet been calculated.
    See Also:
      - Constant Field Values

- ## Constructor Details

  - ### Spring

    protected Spring()
    Used by factory methods to create a `Spring`.
    See Also:
      - `constant(int)`
      - `constant(int, int, int)`
      - `max(javax.swing.Spring, javax.swing.Spring)`
      - `minus(javax.swing.Spring)`
      - `sum(javax.swing.Spring, javax.swing.Spring)`
      - `SpringLayout.Constraints`

- ## Method Details

  - ### getMinimumValue

    public abstract int getMinimumValue()
    Returns the minimum value of this `Spring`.
    Returns:
      the `minimumValue` property of this `Spring`

  - ### getPreferredValue

    public abstract int getPreferredValue()
    Returns the preferred value of this `Spring`.
    Returns:
      the `preferredValue` of this `Spring`

  - ### getMaximumValue

    public abstract int getMaximumValue()
    Returns the maximum value of this `Spring`.
    Returns:
      the `maximumValue` property of this `Spring`

  - ### getValue

    public abstract int getValue()
    Returns the current value of this `Spring`.
    Returns:
      the `value` property of this `Spring`
    See Also:
      - `setValue(int)`

  - ### setValue

    public abstract void setValue(int value)
    Sets the current value of this `Spring` to `value`.
    Parameters:
      `value` - the new setting of the `value` property
    See Also:
      - `getValue()`

  - ### constant

    public static Spring constant(int pref)
    Returns a strut -- a spring whose minimum, preferred, and maximum values each have the value `pref`.
    Parameters:
      `pref` - the minimum, preferred, and maximum values of the new spring
    Returns:
      a spring whose minimum, preferred, and maximum values each have the value `pref`
    See Also:
      - `Spring`

  - ### constant

    public static Spring constant(int min, int pref, int max)
    Returns a spring whose minimum, preferred, and maximum values have the values: `min`, `pref`, and `max` respectively.
    Parameters:
      `min` - the minimum value of the new spring
      `pref` - the preferred value of the new spring
      `max` - the maximum value of the new spring
    Returns:
      a spring whose minimum, preferred, and maximum values have the values: `min`, `pref`, and `max` respectively
    See Also:
      - `Spring`

  - ### minus

    public static Spring minus(Spring s)
    Returns `-s`: a spring running in the opposite direction to `s`.
    Parameters:
      `s` - a `Spring` object
    Returns:
      `-s`: a spring running in the opposite direction to `s`
    See Also:
      - `Spring`

  - ### sum

    public static Spring sum(Spring s1, Spring s2)
    Returns `s1+s2`: a spring representing `s1` and `s2` in series. In a sum, `s3`, of two springs, `s1` and `s2`, the strains of `s1`, `s2`, and `s3` are maintained at the same level (to within the precision implied by their integer values). The strain of a spring in compression is:

                 value - pref
                 ------------
                  pref - min

    and the strain of a spring in tension is:

                 value - pref
                 ------------
                  max - pref

    When `setValue` is called on the sum spring, `s3`, the strain in `s3` is calculated using one of the formulas above. Once the strain of the sum is known, the values of `s1` and `s2` are then set so that they are have a strain equal to that of the sum. The formulas are evaluated so as to take rounding errors into account and ensure that the sum of the values of `s1` and `s2` is exactly equal to the value of `s3`.
    Parameters:
      `s1` - a `Spring` object
      `s2` - a `Spring` object
    Returns:
      `s1+s2`: a spring representing `s1` and `s2` in series
    See Also:
      - `Spring`

  - ### max

    public static Spring max(Spring s1, Spring s2)
    Returns `max(s1, s2)`: a spring whose value is always greater than (or equal to) the values of both `s1` and `s2`.
    Parameters:
      `s1` - a `Spring` object
      `s2` - a `Spring` object
    Returns:
      `max(s1, s2)`: a spring whose value is always greater than (or equal to) the values of both `s1` and `s2`
    See Also:
      - `Spring`

  - ### scale

    public static Spring scale(Spring s, float factor)
    Returns a spring whose minimum, preferred, maximum and value properties are each multiples of the properties of the argument spring, `s`. Minimum and maximum properties are swapped when `factor` is negative (in accordance with the rules of interval arithmetic).

    When factor is, for example, 0.5f the result represents 'the mid-point' of its input - an operation that is useful for centering components in a container.

    Parameters:
      `s` - the spring to scale
      `factor` - amount to scale by.
    Returns:
      a spring whose properties are those of the input spring `s` multiplied by `factor`
    Throws:
      `NullPointerException` - if `s` is null
    Since:
      1.5

  - ### width

    public static Spring width(Component c)
    Returns a spring whose minimum, preferred, maximum and value properties are defined by the widths of the minimumSize, preferredSize, maximumSize and size properties of the supplied component. The returned spring is a 'wrapper' implementation whose methods call the appropriate size methods of the supplied component. The minimum, preferred, maximum and value properties of the returned spring therefore report the current state of the appropriate properties in the component and track them as they change.
    Parameters:
      `c` - Component used for calculating size
    Returns:
      a spring whose properties are defined by the horizontal component of the component's size methods.
    Throws:
      `NullPointerException` - if `c` is null
    Since:
      1.5

  - ### height

    public static Spring height(Component c)
    Returns a spring whose minimum, preferred, maximum and value properties are defined by the heights of the minimumSize, preferredSize, maximumSize and size properties of the supplied component. The returned spring is a 'wrapper' implementation whose methods call the appropriate size methods of the supplied component. The minimum, preferred, maximum and value properties of the returned spring therefore report the current state of the appropriate properties in the component and track them as they change.
    Parameters:
      `c` - Component used for calculating size
    Returns:
      a spring whose properties are defined by the vertical component of the component's size methods.
    Throws:
      `NullPointerException` - if `c` is null
    Since:
      1.5