Java tutorial
/* * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javax.swing; import java.awt.Component; /** * An instance of the <code>Spring</code> class holds three properties that * characterize its behavior: the <em>minimum</em>, <em>preferred</em>, and * <em>maximum</em> values. Each of these properties may be involved in * defining its fourth, <em>value</em>, property based on a series of rules. * <p> * An instance of the <code>Spring</code> 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 <em>preferred</em> and * <em>minimum</em> values, therefore, represents the ease with which the * spring can be compressed and the difference between its <em>maximum</em> * and <em>preferred</em> values, indicates the ease with which the * <code>Spring</code> can be extended. * See the {@link #sum} method for details. * * <p> * By defining simple arithmetic operations on <code>Spring</code>s, * the behavior of a collection of <code>Spring</code>s * can be reduced to that of an ordinary (non-compound) <code>Spring</code>. We define * the "+", "-", <em>max</em>, and <em>min</em> operators on * <code>Spring</code>s so that, in each case, the result is a <code>Spring</code> * whose characteristics bear a useful mathematical relationship to its constituent * springs. * * <p> * A <code>Spring</code> 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 * (<code>[a, b]</code> refers to the interval * from <code>a</code> * to <code>b</code>, * where <code>a <= b</code>). * * <pre> * [a1, b1] + [a2, b2] = [a1 + a2, b1 + b2] * * -[a, b] = [-b, -a] * * max([a1, b1], [a2, b2]) = [max(a1, a2), max(b1, b2)] * </pre> * <p> * * If we denote <code>Spring</code>s as <code>[a, b, c]</code>, * where <code>a <= b <= c</code>, we can define the same * arithmetic operators on <code>Spring</code>s: * * <pre> * [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)] * </pre> * <p> * With both intervals and <code>Spring</code>s we can define "-" and <em>min</em> * in terms of negation: * * <pre> * X - Y = X + (-Y) * * min(X, Y) = -max(-X, -Y) * </pre> * <p> * 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 <code>Spring</code> 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 <em>lazy value</em> * in a functional language. * <p> * If you are implementing a <code>SpringLayout</code> you * can find further information and examples in * <a href="https://docs.oracle.com/javase/tutorial/uiswing/layout/spring.html">How to Use SpringLayout</a>, * a section in <em>The Java Tutorial.</em> * <p> * <strong>Warning:</strong> * 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 <code>java.beans</code> package. * Please see {@link java.beans.XMLEncoder}. * * @see SpringLayout * @see SpringLayout.Constraints * * @author Philip Milne * @since 1.4 */ @SuppressWarnings("serial") // Same-version serialization only public abstract class Spring { /** * An integer value signifying that a property value has not yet been calculated. */ public static final int UNSET = Integer.MIN_VALUE; /** * Used by factory methods to create a <code>Spring</code>. * * @see #constant(int) * @see #constant(int, int, int) * @see #max * @see #minus * @see #sum * @see SpringLayout.Constraints */ protected Spring() { } /** * Returns the <em>minimum</em> value of this <code>Spring</code>. * * @return the <code>minimumValue</code> property of this <code>Spring</code> */ public abstract int getMinimumValue(); /** * Returns the <em>preferred</em> value of this <code>Spring</code>. * * @return the <code>preferredValue</code> of this <code>Spring</code> */ public abstract int getPreferredValue(); /** * Returns the <em>maximum</em> value of this <code>Spring</code>. * * @return the <code>maximumValue</code> property of this <code>Spring</code> */ public abstract int getMaximumValue(); /** * Returns the current <em>value</em> of this <code>Spring</code>. * * @return the <code>value</code> property of this <code>Spring</code> * * @see #setValue */ public abstract int getValue(); /** * Sets the current <em>value</em> of this <code>Spring</code> to <code>value</code>. * * @param value the new setting of the <code>value</code> property * * @see #getValue */ public abstract void setValue(int value); private double range(boolean contract) { return contract ? (getPreferredValue() - getMinimumValue()) : (getMaximumValue() - getPreferredValue()); } /*pp*/ double getStrain() { double delta = (getValue() - getPreferredValue()); return delta / range(getValue() < getPreferredValue()); } /*pp*/ void setStrain(double strain) { setValue(getPreferredValue() + (int) (strain * range(strain < 0))); } /*pp*/ boolean isCyclic(SpringLayout l) { return false; } /*pp*/ static abstract class AbstractSpring extends Spring { protected int size = UNSET; public int getValue() { return size != UNSET ? size : getPreferredValue(); } public final void setValue(int size) { if (this.size == size) { return; } if (size == UNSET) { clear(); } else { setNonClearValue(size); } } protected void clear() { size = UNSET; } protected void setNonClearValue(int size) { this.size = size; } } private static class StaticSpring extends AbstractSpring { protected int min; protected int pref; protected int max; public StaticSpring(int pref) { this(pref, pref, pref); } public StaticSpring(int min, int pref, int max) { this.min = min; this.pref = pref; this.max = max; } public String toString() { return "StaticSpring [" + min + ", " + pref + ", " + max + "]"; } public int getMinimumValue() { return min; } public int getPreferredValue() { return pref; } public int getMaximumValue() { return max; } } private static class NegativeSpring extends Spring { private Spring s; public NegativeSpring(Spring s) { this.s = s; } // Note the use of max value rather than minimum value here. // See the opening preamble on arithmetic with springs. public int getMinimumValue() { return -s.getMaximumValue(); } public int getPreferredValue() { return -s.getPreferredValue(); } public int getMaximumValue() { return -s.getMinimumValue(); } public int getValue() { return -s.getValue(); } public void setValue(int size) { // No need to check for UNSET as // Integer.MIN_VALUE == -Integer.MIN_VALUE. s.setValue(-size); } /*pp*/ boolean isCyclic(SpringLayout l) { return s.isCyclic(l); } } private static class ScaleSpring extends Spring { private Spring s; private float factor; private ScaleSpring(Spring s, float factor) { this.s = s; this.factor = factor; } public int getMinimumValue() { return Math.round((factor < 0 ? s.getMaximumValue() : s.getMinimumValue()) * factor); } public int getPreferredValue() { return Math.round(s.getPreferredValue() * factor); } public int getMaximumValue() { return Math.round((factor < 0 ? s.getMinimumValue() : s.getMaximumValue()) * factor); } public int getValue() { return Math.round(s.getValue() * factor); } public void setValue(int value) { if (value == UNSET) { s.setValue(UNSET); } else { s.setValue(Math.round(value / factor)); } } /*pp*/ boolean isCyclic(SpringLayout l) { return s.isCyclic(l); } } /*pp*/ static class WidthSpring extends AbstractSpring { /*pp*/ Component c; public WidthSpring(Component c) { this.c = c; } public int getMinimumValue() { return c.getMinimumSize().width; } public int getPreferredValue() { return c.getPreferredSize().width; } public int getMaximumValue() { // We will be doing arithmetic with the results of this call, // so if a returned value is Integer.MAX_VALUE we will get // arithmetic overflow. Truncate such values. return Math.min(Short.MAX_VALUE, c.getMaximumSize().width); } } /*pp*/ static class HeightSpring extends AbstractSpring { /*pp*/ Component c; public HeightSpring(Component c) { this.c = c; } public int getMinimumValue() { return c.getMinimumSize().height; } public int getPreferredValue() { return c.getPreferredSize().height; } public int getMaximumValue() { return Math.min(Short.MAX_VALUE, c.getMaximumSize().height); } } /*pp*/ static abstract class SpringMap extends Spring { private Spring s; public SpringMap(Spring s) { this.s = s; } protected abstract int map(int i); protected abstract int inv(int i); public int getMinimumValue() { return map(s.getMinimumValue()); } public int getPreferredValue() { return map(s.getPreferredValue()); } public int getMaximumValue() { return Math.min(Short.MAX_VALUE, map(s.getMaximumValue())); } public int getValue() { return map(s.getValue()); } public void setValue(int value) { if (value == UNSET) { s.setValue(UNSET); } else { s.setValue(inv(value)); } } /*pp*/ boolean isCyclic(SpringLayout l) { return s.isCyclic(l); } } // Use the instance variables of the StaticSpring superclass to // cache values that have already been calculated. /*pp*/ static abstract class CompoundSpring extends StaticSpring { protected Spring s1; protected Spring s2; public CompoundSpring(Spring s1, Spring s2) { super(UNSET); this.s1 = s1; this.s2 = s2; } public String toString() { return "CompoundSpring of " + s1 + " and " + s2; } protected void clear() { super.clear(); min = pref = max = UNSET; s1.setValue(UNSET); s2.setValue(UNSET); } protected abstract int op(int x, int y); public int getMinimumValue() { if (min == UNSET) { min = op(s1.getMinimumValue(), s2.getMinimumValue()); } return min; } public int getPreferredValue() { if (pref == UNSET) { pref = op(s1.getPreferredValue(), s2.getPreferredValue()); } return pref; } public int getMaximumValue() { if (max == UNSET) { max = op(s1.getMaximumValue(), s2.getMaximumValue()); } return max; } public int getValue() { if (size == UNSET) { size = op(s1.getValue(), s2.getValue()); } return size; } /*pp*/ boolean isCyclic(SpringLayout l) { return l.isCyclic(s1) || l.isCyclic(s2); } }; private static class SumSpring extends CompoundSpring { public SumSpring(Spring s1, Spring s2) { super(s1, s2); } protected int op(int x, int y) { return x + y; } protected void setNonClearValue(int size) { super.setNonClearValue(size); s1.setStrain(this.getStrain()); s2.setValue(size - s1.getValue()); } } private static class MaxSpring extends CompoundSpring { public MaxSpring(Spring s1, Spring s2) { super(s1, s2); } protected int op(int x, int y) { return Math.max(x, y); } protected void setNonClearValue(int size) { super.setNonClearValue(size); s1.setValue(size); s2.setValue(size); } } /** * Returns a strut -- a spring whose <em>minimum</em>, <em>preferred</em>, and * <em>maximum</em> values each have the value <code>pref</code>. * * @param pref the <em>minimum</em>, <em>preferred</em>, and * <em>maximum</em> values of the new spring * @return a spring whose <em>minimum</em>, <em>preferred</em>, and * <em>maximum</em> values each have the value <code>pref</code> * * @see Spring */ public static Spring constant(int pref) { return constant(pref, pref, pref); } /** * Returns a spring whose <em>minimum</em>, <em>preferred</em>, and * <em>maximum</em> values have the values: <code>min</code>, <code>pref</code>, * and <code>max</code> respectively. * * @param min the <em>minimum</em> value of the new spring * @param pref the <em>preferred</em> value of the new spring * @param max the <em>maximum</em> value of the new spring * @return a spring whose <em>minimum</em>, <em>preferred</em>, and * <em>maximum</em> values have the values: <code>min</code>, <code>pref</code>, * and <code>max</code> respectively * * @see Spring */ public static Spring constant(int min, int pref, int max) { return new StaticSpring(min, pref, max); } /** * Returns {@code -s}: a spring running in the opposite direction to {@code s}. * * @param s a {@code Spring} object * @return {@code -s}: a spring running in the opposite direction to {@code s} * * @see Spring */ public static Spring minus(Spring s) { return new NegativeSpring(s); } /** * Returns <code>s1+s2</code>: a spring representing <code>s1</code> and <code>s2</code> * in series. In a sum, <code>s3</code>, of two springs, <code>s1</code> and <code>s2</code>, * the <em>strains</em> of <code>s1</code>, <code>s2</code>, and <code>s3</code> are maintained * at the same level (to within the precision implied by their integer <em>value</em>s). * The strain of a spring in compression is: * <pre> * value - pref * ------------ * pref - min * </pre> * and the strain of a spring in tension is: * <pre> * value - pref * ------------ * max - pref * </pre> * When <code>setValue</code> is called on the sum spring, <code>s3</code>, the strain * in <code>s3</code> is calculated using one of the formulas above. Once the strain of * the sum is known, the <em>value</em>s of <code>s1</code> and <code>s2</code> 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 <em>value</em>s of <code>s1</code> and <code>s2</code> is exactly equal to * the <em>value</em> of <code>s3</code>. * * @param s1 a {@code Spring} object * @param s2 a {@code Spring} object * @return <code>s1+s2</code>: a spring representing <code>s1</code> and <code>s2</code> in series * * @see Spring */ public static Spring sum(Spring s1, Spring s2) { return new SumSpring(s1, s2); } /** * Returns {@code max(s1, s2)}: a spring whose value is always greater than (or equal to) * the values of both {@code s1} and {@code s2}. * * @param s1 a {@code Spring} object * @param s2 a {@code Spring} object * @return {@code max(s1, s2)}: a spring whose value is always greater than (or equal to) * the values of both {@code s1} and {@code s2} * @see Spring */ public static Spring max(Spring s1, Spring s2) { return new MaxSpring(s1, s2); } // Remove these, they're not used often and can be created using minus - // as per these implementations. /*pp*/ static Spring difference(Spring s1, Spring s2) { return sum(s1, minus(s2)); } /* public static Spring min(Spring s1, Spring s2) { return minus(max(minus(s1), minus(s2))); } */ /** * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em> * and <em>value</em> properties are each multiples of the properties of the * argument spring, <code>s</code>. Minimum and maximum properties are * swapped when <code>factor</code> is negative (in accordance with the * rules of interval arithmetic). * <p> * 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. * * @param s the spring to scale * @param factor amount to scale by. * @return a spring whose properties are those of the input spring <code>s</code> * multiplied by <code>factor</code> * @throws NullPointerException if <code>s</code> is null * @since 1.5 */ public static Spring scale(Spring s, float factor) { checkArg(s); return new ScaleSpring(s, factor); } /** * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em> * and <em>value</em> properties are defined by the widths of the <em>minimumSize</em>, * <em>preferredSize</em>, <em>maximumSize</em> and <em>size</em> 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. * * @param c Component used for calculating size * @return a spring whose properties are defined by the horizontal component * of the component's size methods. * @throws NullPointerException if <code>c</code> is null * @since 1.5 */ public static Spring width(Component c) { checkArg(c); return new WidthSpring(c); } /** * Returns a spring whose <em>minimum</em>, <em>preferred</em>, <em>maximum</em> * and <em>value</em> properties are defined by the heights of the <em>minimumSize</em>, * <em>preferredSize</em>, <em>maximumSize</em> and <em>size</em> 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. * * @param c Component used for calculating size * @return a spring whose properties are defined by the vertical component * of the component's size methods. * @throws NullPointerException if <code>c</code> is null * @since 1.5 */ public static Spring height(Component c) { checkArg(c); return new HeightSpring(c); } /** * If <code>s</code> is null, this throws an NullPointerException. */ private static void checkArg(Object s) { if (s == null) { throw new NullPointerException("Argument must not be null"); } } }