fixes #181, added drop deparser

Author: wumpz

src/main/java/net/sf/jsqlparser/statement/drop/Drop.java

@@ -33,6 +33,7 @@ public class Drop implements Statement {
 	private String type;
 	private Table name;
 	private List<String> parameters;
+    private boolean ifExists = false;
 
 	@Override
 	public void accept(StatementVisitor statementVisitor) {
@@ -63,9 +64,18 @@ public void setType(String string) {
 		type = string;
 	}
 
+    public boolean isIfExists() {
+        return ifExists;
+    }
+
+    public void setIfExists(boolean ifExists) {
+        this.ifExists = ifExists;
+    }
+
 	@Override
 	public String toString() {
-		String sql = "DROP " + type + " " + name.toString();
+		String sql = "DROP " + type + " "
+           + (ifExists?"IF EXISTS ":"") + name.toString();
 
 		if (parameters != null && parameters.size() > 0) {
 			sql += " " + PlainSelect.getStringList(parameters);

src/main/java/net/sf/jsqlparser/util/deparser/DropDeParser.java

@@ -0,0 +1,60 @@
+/*
+ * #%L
+ * JSQLParser library
+ * %%
+ * Copyright (C) 2004 - 2015 JSQLParser
+ * %%
+ * This program 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 program 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 Lesser Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Lesser Public 
+ * License along with this program.  If not, see
+ * <http://www.gnu.org/licenses/lgpl-2.1.html>.
+ * #L%
+ */
+package net.sf.jsqlparser.util.deparser;
+
+
+import net.sf.jsqlparser.statement.drop.Drop;
+import net.sf.jsqlparser.statement.select.PlainSelect;
+
+/**
+ * @author tw
+ */
+public class DropDeParser {
+
+    private StringBuilder buffer;
+
+	public DropDeParser(StringBuilder buffer) {
+		this.buffer = buffer;
+	}
+
+	public void deParse(Drop drop) {
+		buffer.append("DROP ");
+        buffer.append(drop.getType());
+        if (drop.isIfExists())
+            buffer.append(" IF EXISTS");
+
+		buffer.append(" ").append(drop.getName());
+        
+        if (drop.getParameters() != null && drop.getParameters().size() > 0) {
+			buffer.append(" ").append(PlainSelect.getStringList(drop.getParameters()));
+		}
+	}
+
+	public StringBuilder getBuffer() {
+		return buffer;
+	}
+
+	public void setBuffer(StringBuilder buffer) {
+		this.buffer = buffer;
+	}
+
+}

src/main/java/net/sf/jsqlparser/util/deparser/StatementDeParser.java

@@ -79,7 +79,8 @@ public void visit(Delete delete) {
 
     @Override
     public void visit(Drop drop) {
-        // TODO Auto-generated method stub
+        DropDeParser dropDeParser = new DropDeParser(buffer);
+        dropDeParser.deParse(drop);
     }
 
     @Override
@@ -90,7 +91,6 @@ public void visit(Insert insert) {
         selectDeParser.setExpressionVisitor(expressionDeParser);
         InsertDeParser insertDeParser = new InsertDeParser(expressionDeParser, selectDeParser, buffer);
         insertDeParser.deParse(insert);
-
     }
 
     @Override

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -2739,6 +2739,9 @@ Drop Drop():
 		tk=<K_INDEX>
 	)
     { drop.setType(tk.image); }
+
+    [<K_IF> <K_EXISTS> {drop.setIfExists(true);} ]
+
 	name = Table() { drop.setName(name); }
 	((tk=<S_IDENTIFIER> | tk=<K_CASCADE>) { dropArgs.add(tk.image); })*
 

src/test/java/net/sf/jsqlparser/test/drop/DropTest.java

@@ -36,4 +36,8 @@ public void testDrop2() throws JSQLParserException {
         assertEquals("TABLE", drop.getType());
         assertEquals("\"testtable\"", drop.getName().getFullyQualifiedName());
     }
+    
+    public void testDropIfExists() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed("DROP TABLE IF EXISTS my_table");
+    }
 }