Java example source code file (Choice.java)

This example Java source code file (Choice.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

accessibleaction, accessibleawtchoice, awt, choice, choicepeer, event, eventlistener, headlessexception, illegalargumentexception, itemevent, itemlistener, itemselectable, object, string, util, vector

The Choice.java Java example source code

/*
 * Copyright (c) 1995, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package java.awt;

import java.util.*;
import java.awt.peer.ChoicePeer;
import java.awt.event.*;
import java.util.EventListener;
import java.io.ObjectOutputStream;
import java.io.ObjectInputStream;
import java.io.IOException;

import javax.accessibility.*;


/**
 * The <code>Choice class presents a pop-up menu of choices.
 * The current choice is displayed as the title of the menu.
 * <p>
 * The following code example produces a pop-up menu:
 *
 * <hr>
 * Choice ColorChooser = new Choice();
 * ColorChooser.add("Green");
 * ColorChooser.add("Red");
 * ColorChooser.add("Blue");
 * </pre>

 * <p>
 * After this choice menu has been added to a panel,
 * it appears as follows in its normal state:
 * <p>
 * <img src="doc-files/Choice-1.gif" alt="The following text describes the graphic"
 * style="float:center; margin: 7px 10px;">
 * <p>
 * In the picture, <code>"Green" is the current choice.
 * Pushing the mouse button down on the object causes a menu to
 * appear with the current choice highlighted.
 * <p>
 * Some native platforms do not support arbitrary resizing of
 * <code>Choice components and the behavior of
 * <code>setSize()/getSize() is bound by
 * such limitations.
 * Native GUI <code>Choice components' size are often bound by such
 * attributes as font size and length of items contained within
 * the <code>Choice.
 * <p>
 * @author      Sami Shaio
 * @author      Arthur van Hoff
 * @since       JDK1.0
 */
public class Choice extends Component implements ItemSelectable, Accessible {
    /**
     * The items for the <code>Choice.
     * This can be a <code>null value.
     * @serial
     * @see #add(String)
     * @see #addItem(String)
     * @see #getItem(int)
     * @see #getItemCount()
     * @see #insert(String, int)
     * @see #remove(String)
     */
    Vector<String> pItems;

    /**
     * The index of the current choice for this <code>Choice
     * or -1 if nothing is selected.
     * @serial
     * @see #getSelectedItem()
     * @see #select(int)
     */
    int selectedIndex = -1;

    transient ItemListener itemListener;

    private static final String base = "choice";
    private static int nameCounter = 0;

    /*
     * JDK 1.1 serialVersionUID
     */
    private static final long serialVersionUID = -4075310674757313071L;

    static {
        /* ensure that the necessary native libraries are loaded */
        Toolkit.loadLibraries();
        /* initialize JNI field and method ids */
        if (!GraphicsEnvironment.isHeadless()) {
            initIDs();
        }
    }

    /**
     * Creates a new choice menu. The menu initially has no items in it.
     * <p>
     * By default, the first item added to the choice menu becomes the
     * selected item, until a different selection is made by the user
     * by calling one of the <code>select methods.
     * @exception HeadlessException if GraphicsEnvironment.isHeadless()
     * returns true
     * @see       java.awt.GraphicsEnvironment#isHeadless
     * @see       #select(int)
     * @see       #select(java.lang.String)
     */
    public Choice() throws HeadlessException {
        GraphicsEnvironment.checkHeadless();
        pItems = new Vector<>();
    }

    /**
     * Constructs a name for this component.  Called by
     * <code>getName when the name is null.
     */
    String constructComponentName() {
        synchronized (Choice.class) {
            return base + nameCounter++;
        }
    }

    /**
     * Creates the <code>Choice's peer.  This peer allows us
     * to change the look
     * of the <code>Choice without changing its functionality.
     * @see     java.awt.Toolkit#createChoice(java.awt.Choice)
     * @see     java.awt.Component#getToolkit()
     */
    public void addNotify() {
        synchronized (getTreeLock()) {
            if (peer == null)
                peer = getToolkit().createChoice(this);
            super.addNotify();
        }
    }

    /**
     * Returns the number of items in this <code>Choice menu.
     * @return the number of items in this <code>Choice menu
     * @see     #getItem
     * @since   JDK1.1
     */
    public int getItemCount() {
        return countItems();
    }

    /**
     * @deprecated As of JDK version 1.1,
     * replaced by <code>getItemCount().
     */
    @Deprecated
    public int countItems() {
        return pItems.size();
    }

    /**
     * Gets the string at the specified index in this
     * <code>Choice menu.
     * @param      index the index at which to begin
     * @see        #getItemCount
     */
    public String getItem(int index) {
        return getItemImpl(index);
    }

    /*
     * This is called by the native code, so client code can't
     * be called on the toolkit thread.
     */
    final String getItemImpl(int index) {
        return pItems.elementAt(index);
    }

    /**
     * Adds an item to this <code>Choice menu.
     * @param      item    the item to be added
     * @exception  NullPointerException   if the item's value is
     *                  <code>null
     * @since      JDK1.1
     */
    public void add(String item) {
        addItem(item);
    }

    /**
     * Obsolete as of Java 2 platform v1.1.  Please use the
     * <code>add method instead.
     * <p>
     * Adds an item to this <code>Choice menu.
     * @param item the item to be added
     * @exception NullPointerException if the item's value is equal to
     *          <code>null
     */
    public void addItem(String item) {
        synchronized (this) {
            insertNoInvalidate(item, pItems.size());
        }

        // This could change the preferred size of the Component.
        invalidateIfValid();
    }

    /**
     * Inserts an item to this <code>Choice,
     * but does not invalidate the <code>Choice.
     * Client methods must provide their own synchronization before
     * invoking this method.
     * @param item the item to be added
     * @param index the new item position
     * @exception NullPointerException if the item's value is equal to
     *          <code>null
     */
    private void insertNoInvalidate(String item, int index) {
        if (item == null) {
            throw new
                NullPointerException("cannot add null item to Choice");
        }
        pItems.insertElementAt(item, index);
        ChoicePeer peer = (ChoicePeer)this.peer;
        if (peer != null) {
            peer.add(item, index);
        }
        // no selection or selection shifted up
        if (selectedIndex < 0 || selectedIndex >= index) {
            select(0);
        }
    }


    /**
     * Inserts the item into this choice at the specified position.
     * Existing items at an index greater than or equal to
     * <code>index are shifted up by one to accommodate
     * the new item.  If <code>index is greater than or
     * equal to the number of items in this choice,
     * <code>item is added to the end of this choice.
     * <p>
     * If the item is the first one being added to the choice,
     * then the item becomes selected.  Otherwise, if the
     * selected item was one of the items shifted, the first
     * item in the choice becomes the selected item.  If the
     * selected item was no among those shifted, it remains
     * the selected item.
     * @param item the non-<code>null item to be inserted
     * @param index the position at which the item should be inserted
     * @exception IllegalArgumentException if index is less than 0
     */
    public void insert(String item, int index) {
        synchronized (this) {
            if (index < 0) {
                throw new IllegalArgumentException("index less than zero.");
            }
            /* if the index greater than item count, add item to the end */
            index = Math.min(index, pItems.size());

            insertNoInvalidate(item, index);
        }

        // This could change the preferred size of the Component.
        invalidateIfValid();
    }

    /**
     * Removes the first occurrence of <code>item
     * from the <code>Choice menu.  If the item
     * being removed is the currently selected item,
     * then the first item in the choice becomes the
     * selected item.  Otherwise, the currently selected
     * item remains selected (and the selected index is
     * updated accordingly).
     * @param      item  the item to remove from this <code>Choice menu
     * @exception  IllegalArgumentException  if the item doesn't
     *                     exist in the choice menu
     * @since      JDK1.1
     */
    public void remove(String item) {
        synchronized (this) {
            int index = pItems.indexOf(item);
            if (index < 0) {
                throw new IllegalArgumentException("item " + item +
                                                   " not found in choice");
            } else {
                removeNoInvalidate(index);
            }
        }

        // This could change the preferred size of the Component.
        invalidateIfValid();
    }

    /**
     * Removes an item from the choice menu
     * at the specified position.  If the item
     * being removed is the currently selected item,
     * then the first item in the choice becomes the
     * selected item.  Otherwise, the currently selected
     * item remains selected (and the selected index is
     * updated accordingly).
     * @param      position the position of the item
     * @throws IndexOutOfBoundsException if the specified
     *          position is out of bounds
     * @since      JDK1.1
     */
    public void remove(int position) {
        synchronized (this) {
            removeNoInvalidate(position);
        }

        // This could change the preferred size of the Component.
        invalidateIfValid();
    }

    /**
     * Removes an item from the <code>Choice at the
     * specified position, but does not invalidate the <code>Choice.
     * Client methods must provide their
     * own synchronization before invoking this method.
     * @param      position   the position of the item
     */
    private void removeNoInvalidate(int position) {
        pItems.removeElementAt(position);
        ChoicePeer peer = (ChoicePeer)this.peer;
        if (peer != null) {
            peer.remove(position);
        }
        /* Adjust selectedIndex if selected item was removed. */
        if (pItems.size() == 0) {
            selectedIndex = -1;
        } else if (selectedIndex == position) {
            select(0);
        } else if (selectedIndex > position) {
            select(selectedIndex-1);
        }
    }


    /**
     * Removes all items from the choice menu.
     * @see       #remove
     * @since     JDK1.1
     */
    public void removeAll() {
        synchronized (this) {
            if (peer != null) {
                ((ChoicePeer)peer).removeAll();
            }
            pItems.removeAllElements();
            selectedIndex = -1;
        }

        // This could change the preferred size of the Component.
        invalidateIfValid();
    }

    /**
     * Gets a representation of the current choice as a string.
     * @return    a string representation of the currently
     *                     selected item in this choice menu
     * @see       #getSelectedIndex
     */
    public synchronized String getSelectedItem() {
        return (selectedIndex >= 0) ? getItem(selectedIndex) : null;
    }

    /**
     * Returns an array (length 1) containing the currently selected
     * item.  If this choice has no items, returns <code>null.
     * @see ItemSelectable
     */
    public synchronized Object[] getSelectedObjects() {
        if (selectedIndex >= 0) {
            Object[] items = new Object[1];
            items[0] = getItem(selectedIndex);
            return items;
        }
        return null;
    }

    /**
     * Returns the index of the currently selected item.
     * If nothing is selected, returns -1.
     *
     * @return the index of the currently selected item, or -1 if nothing
     *  is currently selected
     * @see #getSelectedItem
     */
    public int getSelectedIndex() {
        return selectedIndex;
    }

    /**
     * Sets the selected item in this <code>Choice menu to be the
     * item at the specified position.
     *
     * <p>Note that this method should be primarily used to
     * initially select an item in this component.
     * Programmatically calling this method will <i>not trigger
     * an <code>ItemEvent.  The only way to trigger an
     * <code>ItemEvent is by user interaction.
     *
     * @param      pos      the position of the selected item
     * @exception  IllegalArgumentException if the specified
     *                            position is greater than the
     *                            number of items or less than zero
     * @see        #getSelectedItem
     * @see        #getSelectedIndex
     */
    public synchronized void select(int pos) {
        if ((pos >= pItems.size()) || (pos < 0)) {
            throw new IllegalArgumentException("illegal Choice item position: " + pos);
        }
        if (pItems.size() > 0) {
            selectedIndex = pos;
            ChoicePeer peer = (ChoicePeer)this.peer;
            if (peer != null) {
                peer.select(pos);
            }
        }
    }

    /**
     * Sets the selected item in this <code>Choice menu
     * to be the item whose name is equal to the specified string.
     * If more than one item matches (is equal to) the specified string,
     * the one with the smallest index is selected.
     *
     * <p>Note that this method should be primarily used to
     * initially select an item in this component.
     * Programmatically calling this method will <i>not trigger
     * an <code>ItemEvent.  The only way to trigger an
     * <code>ItemEvent is by user interaction.
     *
     * @param       str     the specified string
     * @see         #getSelectedItem
     * @see         #getSelectedIndex
     */
    public synchronized void select(String str) {
        int index = pItems.indexOf(str);
        if (index >= 0) {
            select(index);
        }
    }

    /**
     * Adds the specified item listener to receive item events from
     * this <code>Choice menu.  Item events are sent in response
     * to user input, but not in response to calls to <code>select.
     * If l is <code>null, no exception is thrown and no action
     * is performed.
     * <p>Refer to  for details on AWT's threading model.
     * @param         l    the item listener
     * @see           #removeItemListener
     * @see           #getItemListeners
     * @see           #select
     * @see           java.awt.event.ItemEvent
     * @see           java.awt.event.ItemListener
     * @since         JDK1.1
     */
    public synchronized void addItemListener(ItemListener l) {
        if (l == null) {
           return;
        }
        itemListener = AWTEventMulticaster.add(itemListener, l);
        newEventsOnly = true;
    }

    /**
     * Removes the specified item listener so that it no longer receives
     * item events from this <code>Choice menu.
     * If l is <code>null, no exception is thrown and no
     * action is performed.
     * <p>Refer to  for details on AWT's threading model.
     * @param         l    the item listener
     * @see           #addItemListener
     * @see           #getItemListeners
     * @see           java.awt.event.ItemEvent
     * @see           java.awt.event.ItemListener
     * @since         JDK1.1
     */
    public synchronized void removeItemListener(ItemListener l) {
        if (l == null) {
            return;
        }
        itemListener = AWTEventMulticaster.remove(itemListener, l);
    }

    /**
     * Returns an array of all the item listeners
     * registered on this choice.
     *
     * @return all of this choice's <code>ItemListeners
     *         or an empty array if no item
     *         listeners are currently registered
     *
     * @see           #addItemListener
     * @see           #removeItemListener
     * @see           java.awt.event.ItemEvent
     * @see           java.awt.event.ItemListener
     * @since 1.4
     */
    public synchronized ItemListener[] getItemListeners() {
        return getListeners(ItemListener.class);
    }

    /**
     * Returns an array of all the objects currently registered
     * as <code>FooListeners
     * upon this <code>Choice.
     * <code>FooListeners are registered using the
     * <code>addFooListener method.
     *
     * <p>
     * You can specify the <code>listenerType argument
     * with a class literal, such as
     * <code>FooListener.class.
     * For example, you can query a
     * <code>Choice c
     * for its item listeners with the following code:
     *
     * <pre>ItemListener[] ils = (ItemListener[])(c.getListeners(ItemListener.class));