Java example source code file (Painter.java)

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awt, painter

The Painter.java Java example source code

/*
 * Copyright (c) 2005, 2013, 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
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package javax.swing;

import java.awt.Graphics2D;

/**
 * <p>A painting delegate. The Painter interface defines exactly one method,
 * <code>paint. It is used in situations where the developer can change
 * the painting routine of a component without having to resort to subclassing
 * the component. It is also generically useful when doing any form of painting
 * delegation.</p>
 *
 * <p>Painters are simply encapsulations of Java2D code and make
 * it fairly trivial to reuse existing <code>Painters or to combine
 * them together. Implementations of this interface are also trivial to write,
 * such that if you can't find a <code>Painter that does what you need,
 * you can write one with minimal effort. Writing a <code>Painter requires
 * knowledge of Java2D.</p>
 *
 * <p>A Painter may be created with a type parameter. This type will be
 * expected in the <code>paint method. For example, you may wish to write a
 * <code>Painter that only works with subclasses of {@link java.awt.Component}.
 * In that case, when the <code>Painter is declared, you may declare that
 * it requires a <code>Component, allowing the paint method to be type safe. Ex:
 * <pre>
 * {@code
 * Painter<Component> p = new Painter() {
 *     public void paint(Graphics2D g, Component c, int width, int height) {
 *         g.setColor(c.getBackground());
 *         //and so forth
 *     }
 * }
 * }
 * </pre>
 *
 * <p>This interface makes no guarantees of threadsafety.

 *
 * @author rbair
 */
public interface Painter<T> {
    /**
     * <p>Renders to the given {@link java.awt.Graphics2D} object. Implementations
     * of this method <em>may modify state on the Graphics2D, and are not
     * required to restore that state upon completion. In most cases, it is recommended
     * that the caller pass in a scratch graphics object. The <code>Graphics2D
     * must never be null.</p>
     *
     * <p>State on the graphics object may be honored by the paint method,
     * but may not be. For instance, setting the antialiasing rendering hint on the
     * graphics may or may not be respected by the <code>Painter implementation.

     *
     * <p>The supplied object parameter acts as an optional configuration argument.
     * For example, it could be of type <code>Component. A Painter
     * that expected it could then read state from that <code>Component and
     * use the state for painting. For example, an implementation may read the
     * backgroundColor and use that.</p>
     *
     * <p>Generally, to enhance reusability, most standard Painters ignore
     * this parameter. They can thus be reused in any context. The <code>object
     * may be null. Implementations must not throw a NullPointerException if the object
     * parameter is null.</p>
     *
     * <p>Finally, the width and height arguments specify the
     * width and height that the <code>Painter should paint into. More
     * specifically, the specified width and height instruct the painter that it should
     * paint fully within this width and height. Any specified clip on the
     * <code>g param will further constrain the region.

     *
     * <p>For example, suppose I have a Painter implementation that draws
     * a gradient. The gradient goes from white to black. It "stretches" to fill the
     * painted region. Thus, if I use this <code>Painter to paint a 500 x 500
     * region, the far left would be black, the far right would be white, and a smooth
     * gradient would be painted between. I could then, without modification, reuse the
     * <code>Painter to paint a region that is 20x20 in size. This region would
     * also be black on the left, white on the right, and a smooth gradient painted
     * between.</p>
     *
     * @param g The Graphics2D to render to. This must not be null.
     * @param object an optional configuration parameter. This may be null.
     * @param width width of the area to paint.
     * @param height height of the area to paint.
     */
    public void paint(Graphics2D g, T object, int width, int height);
}