Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.lang3; /** * <p>An enum representing all the versions of the Java specification. * This is intended to mirror available values from the * <em>java.specification.version</em> System property. </p> * * @since 3.0 * @version $Id$ */ public enum JavaVersion { /** * The Java version reported by Android. This is not an official Java version number. */ JAVA_0_9(1.5f, "0.9"), /** * Java 1.1. */ JAVA_1_1(1.1f, "1.1"), /** * Java 1.2. */ JAVA_1_2(1.2f, "1.2"), /** * Java 1.3. */ JAVA_1_3(1.3f, "1.3"), /** * Java 1.4. */ JAVA_1_4(1.4f, "1.4"), /** * Java 1.5. */ JAVA_1_5(1.5f, "1.5"), /** * Java 1.6. */ JAVA_1_6(1.6f, "1.6"), /** * Java 1.7. */ JAVA_1_7(1.7f, "1.7"), /** * Java 1.8. */ JAVA_1_8(1.8f, "1.8"), /** * Java 1.9. */ JAVA_1_9(1.9f, "1.9"), /** * Java 1.x, x > 9. Mainly introduced to avoid to break when a new version of Java is used. */ JAVA_RECENT(maxVersion(), Float.toString(maxVersion())); /** * The float value. */ private final float value; /** * The standard name. */ private final String name; /** * Constructor. * * @param value the float value * @param name the standard name, not null */ JavaVersion(final float value, final String name) { this.value = value; this.name = name; } //----------------------------------------------------------------------- /** * <p>Whether this version of Java is at least the version of Java passed in.</p> * * <p>For example:<br> * {@code myVersion.atLeast(JavaVersion.JAVA_1_4)}<p> * * @param requiredVersion the version to check against, not null * @return true if this version is equal to or greater than the specified version */ public boolean atLeast(final JavaVersion requiredVersion) { return this.value >= requiredVersion.value; } /** * Transforms the given string with a Java version number to the * corresponding constant of this enumeration class. This method is used * internally. * * @param nom the Java version as string * @return the corresponding enumeration constant or <b>null</b> if the * version is unknown */ // helper for static importing static JavaVersion getJavaVersion(final String nom) { return get(nom); } /** * Transforms the given string with a Java version number to the * corresponding constant of this enumeration class. This method is used * internally. * * @param nom the Java version as string * @return the corresponding enumeration constant or <b>null</b> if the * version is unknown */ static JavaVersion get(final String nom) { if ("0.9".equals(nom)) { return JAVA_0_9; } else if ("1.1".equals(nom)) { return JAVA_1_1; } else if ("1.2".equals(nom)) { return JAVA_1_2; } else if ("1.3".equals(nom)) { return JAVA_1_3; } else if ("1.4".equals(nom)) { return JAVA_1_4; } else if ("1.5".equals(nom)) { return JAVA_1_5; } else if ("1.6".equals(nom)) { return JAVA_1_6; } else if ("1.7".equals(nom)) { return JAVA_1_7; } else if ("1.8".equals(nom)) { return JAVA_1_8; } else if ("1.9".equals(nom)) { return JAVA_1_9; } if (nom == null) { return null; } final float v = toFloatVersion(nom); if ((v - 1.) < 1.) { // then we need to check decimals > .9 final int firstComma = Math.max(nom.indexOf('.'), nom.indexOf(',')); final int end = Math.max(nom.length(), nom.indexOf(',', firstComma)); if (Float.parseFloat(nom.substring(firstComma + 1, end)) > .9f) { return JAVA_RECENT; } } return null; } //----------------------------------------------------------------------- /** * <p>The string value is overridden to return the standard name.</p> * * <p>For example, <code>"1.5"</code>.</p> * * @return the name, not null */ @Override public String toString() { return name; } /** * Gets the Java Version from the system or 2.0 if the {@code java.version} system property is not set. * * @return the value of {@code java.version} system property or 2.0 if it is not set. */ private static float maxVersion() { final float v = toFloatVersion(System.getProperty("java.version", "2.0")); if (v > 0) { return v; } return 2f; } /** * Parses a float value from a String. * * @param value the String to parse. * @return the float value represented by teh string or -1 if the given String can not be parsed. */ private static float toFloatVersion(final String value) { final String[] toParse = value.split("\\."); if (toParse.length >= 2) { try { return Float.parseFloat(toParse[0] + '.' + toParse[1]); } catch (final NumberFormatException nfe) { // no-op, let use default } } return -1; } }