Java tutorial
/* * The MIT License * * Copyright (c) 2012, Ninja Squad * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN * THE SOFTWARE. */ package com.ninja_squad.core.presentation; import java.io.Serializable; import javax.annotation.Nonnull; import com.google.common.base.Function; import com.google.common.base.Functions; import com.google.common.base.Objects; import com.google.common.base.Preconditions; import com.ninja_squad.core.i18n.EnumResources; /** * <p>An option, that can be chosen in a select/combo box. An option has a value and a label. The value can be of * any type, and the label, which is typically internationalized, is what is displayed to the end user. * </p> * <p>Two options are equal if their values are equal. A special "null option" is often displayed at the beginning * of the list of options, to force the user to make a choice. Such a "null option" has a null value, and a * customizable label. Such null options are constructed using one of the <code>nullOption()</code> factory methods. * Two null options are always equal to each other, regardless of their label.</p> * <p> * If the type of the value of the option is immutable, then so is the Option wrapping it. * </p> * @author JB Nizet * * @param <V> The type of the value of the option. */ public final class Option<V> implements Serializable { @SuppressWarnings({ "rawtypes", "unchecked" }) private static final Option NULL_SPACE_OPTION = new Option(null, " "); @SuppressWarnings({ "rawtypes", "unchecked" }) private static final Option NULL_EMPTY_OPTION = new Option(null, ""); private final V value; private final String label; private Option(V value, String label) { this.value = value; this.label = label; } /** * Creates a new option * @param value the value of the option * @param label the label of the option * @return the created option */ public static <V> Option<V> newOption(@Nonnull V value, @Nonnull String label) { Preconditions.checkNotNull(value, "value may not be null"); Preconditions.checkNotNull(label, "label may not be null"); return new Option<V>(value, label); } /** * Creates a new option from its value and the <code>toString</code> function to set its label * @param value the value of the option * @return the created option * @see #forValue(Object, Function) */ public static <V> Option<V> forValue(@Nonnull V value) { return forValue(value, Functions.toStringFunction()); } /** * Creates a new option from its value and a function * @param value the value of the option * @param valueToLabel the function which is used to get the label corresponding to the value * @return the created option */ public static <V> Option<V> forValue(@Nonnull V value, @Nonnull Function<? super V, String> valueToLabel) { Preconditions.checkNotNull(value, "value may not be null"); Preconditions.checkNotNull(valueToLabel, "label may not be null"); return Option.<V>valueToOptionFunction(valueToLabel).apply(value); } /** * Creates a new option with the given enum constant as value, and its internationalized label as value. * @param enumConstant the enum to transform into options * @param enumResources the {@link EnumResources} instance used to get the label associated to the enum constant * @return the created option */ public static <V extends Enum<V>> Option<V> forEnum(@Nonnull V enumConstant, @Nonnull final EnumResources enumResources) { Preconditions.checkNotNull(enumConstant, "enumConstant may not be null"); Preconditions.checkNotNull(enumResources, "enumResources may not be null"); return Option.<V>enumToOptionFunction(enumResources).apply(enumConstant); } /** * Creates a null option with the given label * @param label the label of the null option * @return the created null option. */ public static <V> Option<V> nullOption(@Nonnull String label) { Preconditions.checkNotNull(label, "label may not be null"); return new Option<V>(null, label); } /** * Creates a null option with a single space char as label. This is useful when used in a Swing combo box, because * an empty Strin results in an option that has a tiny height, and thus goes unnoticed and is not easily selectable. * @return a constant null option */ @SuppressWarnings("unchecked") public static <V> Option<V> nullSpaceOption() { return NULL_SPACE_OPTION; } /** * Creates a null option with a single space char as label. This is useful when used in a Swing combo box, because * an empty Strin results in an option that has a tiny height, and thus goes unnoticed and is not easily selectable. * @return a constant null option */ @SuppressWarnings("unchecked") public static <V> Option<V> nullEmptyOption() { return NULL_EMPTY_OPTION; } /** * Tests is this option is a null option * @return true if the value is <code>null</code>, false otherwise. */ public boolean isNull() { return this.value == null; } /** * Returns the value of this option * @return the value of this option, which is <code>null</code> if the option is a null option */ public V getValue() { return value; } /** * Returns the label of this option * @return the label of this option */ public String getLabel() { return label; } /** * Returns <code>true</code> iff theobject is an option whose value is equal to this option's value, or if * both options are null options */ @Override public boolean equals(Object obj) { if (obj == this) { return true; } if (!(obj instanceof Option<?>)) { return false; } Option<?> option = (Option<?>) obj; return Objects.equal(this.value, option.value); } @Override public int hashCode() { return Objects.hashCode(value); } /** * Returns the label of this option. Instances of this class can thus be used as elements of a Swing combo box, * without needing any specific renderer. */ @Override public String toString() { return label; } static <V> Function<V, Option<V>> valueToOptionFunction( @Nonnull final Function<? super V, String> valueToLabel) { return new Function<V, Option<V>>() { @edu.umd.cs.findbugs.annotations.SuppressWarnings(value = "NP", justification = "if null, it'll throw a NPE as documented") @Override public Option<V> apply(V input) { String generatedLabel = valueToLabel.apply(input); return newOption(input, generatedLabel); } }; } static <V extends Enum<V>> Function<V, Option<V>> enumToOptionFunction( @Nonnull final EnumResources enumResources) { return new Function<V, Option<V>>() { @Override @edu.umd.cs.findbugs.annotations.SuppressWarnings(value = "NP", justification = "if null, it'll throw a NPE as documented") public Option<V> apply(V input) { return newOption(input, enumResources.getString(input)); } }; } }