Java tutorial
/* * JBoss, Home of Professional Open Source. * See the COPYRIGHT.txt file distributed with this work for information * regarding copyright ownership. Some portions may be licensed * to Red Hat, Inc. under one or more contributor license agreements. * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * This library 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 * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA * 02110-1301 USA. */ package org.jboss.bqt.jdbc.sql.lang; import org.apache.commons.lang.StringUtils; /** * This is the server's representation of a metadata symbol. The only thing * a symbol has to have is a name. This name relates only to how a symbol is * specified in a user's query and does not necessarily relate to any * actual metadata identifier (although it may). Subclasses of this class * provide specialized instances of symbol for various circumstances in a * user's query. In the context of a single query, a symbol's name has * a unique meaning although it may be used more than once in some circumstances. */ public abstract class Symbol implements LanguageObject { /** * Name of the symbol * * Prior to resolving it is the name as entered in the query, * after resolving it is the fully qualified name. */ private String name; /** * upper case of name */ private String canonicalName; /** * Prior to resolving null, after resolving it is the exact string * entered in the query. * * The AliasGenerator can also set this value as necessary for the data tier. */ private String outputName; /** * Constructor to be used for cloning instances. Calls to String.toUpperCase() to generate the canonical names * were the big performance hit during cloning, so this method allows subclasses to simply pass in the canonical name * to avoid toUpperCase(). * @param name * @param canonicalName * @since 4.3 */ protected Symbol(String name, String canonicalName) { this.name = name; this.canonicalName = canonicalName; } /** * Construct a symbol with a name. * @param name Name of the symbol * @throws IllegalArgumentException If name is null */ public Symbol(String name) { setName(name); } /** * Change the symbol's name. This will change the symbol's hash code * and canonical name!!!!!!!!!!!!!!!!! If this symbol is in a hashed * collection, it will be lost! * @param name New name */ public void setName(String name) { if (name == null) { throw new IllegalArgumentException("Error: called setName with null value"); //$NON-NLS-1$ } this.name = name; this.outputName = null; // Canonical name is lazily created this.canonicalName = null; } /** * Get the name of the symbol * @return Name of the symbol, never null */ public String getName() { return this.name; } /** * Get canonical name for comparisons * @return Canonical name for comparisons */ public String getCanonicalName() { // PERFORMANCE1: String.toUpperCase() is an expensive call, and calls from this class are the largest component // of the total toUpperCase() calls, so we are lazily performing the toUpperCase and calculating the hash. computeCanonicalNameAndHash(); return this.canonicalName; } /** * Returns true if this symbol has been completely resolved with respect * to actual runtime metadata. A resolved symbol has been validated that * it refers to actual metadata and will have references to the real metadata * IDs if necessary. Different types of symbols determine their resolution * in different ways, so this method is abstract and must be implemented * by subclasses. * @return True if resolved with runtime metadata */ public abstract boolean isResolved(); /** * Returns string representation of this symbol. * @return String representing the symbol */ public String toString() { return "Symbal.toString() not fully implemented"; // return SQLStringVisitor.getSQLString(this); } /** * Return a hash code for this symbol. * @return Hash code */ public int hashCode() { computeCanonicalNameAndHash(); // Return cached hash code return this.canonicalName.hashCode(); } /** * Compare the symbol based ONLY on name. Symbols are not compared based on * their underlying physical metadata IDs but rather on their representation * in the context of a particular query. Case is not important when comparing * symbol names. * @param obj Other object * @return True if other obj is a Symbol (or subclass) and name is equal */ public boolean equals(Object obj) { if (obj == this) { return true; } if (!(obj instanceof Symbol)) { return false; } return ((Symbol) obj).getCanonicalName().equals(getCanonicalName()); } /** * Return a copy of this object. * @return Object */ public abstract Object clone(); protected String getCanonical() { return canonicalName; } private void computeCanonicalNameAndHash() { if (canonicalName == null) { canonicalName = StringUtils.upperCase(name); } } public String getOutputName() { return this.outputName == null ? getName() : this.outputName; } public void setOutputName(String outputName) { this.outputName = outputName; } }