added -package option.

tool/playground/A.g4

@@ -1,6 +1,6 @@
 grammar A;
 
-s : INT { System.out.println($ctx.getStart());} ;
+s : INT { System.out.println($start.getText());} ;
 
 INT : [0-9]+ ;
 WS : [ \t\n]+ -> skip ;

tool/resources/org/antlr/v4/tool/templates/codegen/Java/Java.stg

@@ -14,7 +14,11 @@ javaTypeInitMap ::= [
 
 ParserFile(file, parser, namedActions) ::= <<
 // $ANTLR ANTLRVersion> <file.fileName> generatedTimestamp>
+<if(file.genPackage)>
+package <file.genPackage>;
+<else>
 <namedActions.header>
+<endif>
 import org.antlr.v4.runtime.atn.*;
 import org.antlr.v4.runtime.dfa.DFA;
 import org.antlr.v4.runtime.*;
@@ -676,7 +680,11 @@ _prevctx.stop = _input.LT(-1);
 
 LexerFile(lexerFile, lexer, namedActions) ::= <<
 // $ANTLR ANTLRVersion> <lexerFile.fileName> generatedTimestamp>
+<if(lexerFile.genPackage)>
+package <lexerFile.genPackage>;
+<else>
 <namedActions.header>
+<endif>
 import org.antlr.v4.runtime.Lexer;
 import org.antlr.v4.runtime.CharStream;
 import org.antlr.v4.runtime.Token;

tool/src/org/antlr/v4/Tool.java

@@ -126,6 +126,7 @@ public class Tool {
 	public boolean verbose_dfa = false;
 	public boolean gen_listener = true;
 	public boolean gen_visitor = false;
+	public String genPackage = null;
 	public Map<String, String> grammarOptions = null;
 
     public static Option[] optionDefs = {
@@ -144,6 +145,7 @@ public class Tool {
 		new Option("gen_listener",		"-no-listener", "don't generate parse tree listener"),
 		new Option("gen_visitor",		"-visitor", "generate parse tree visitor"),
 		new Option("gen_visitor",		"-no-visitor", "don't generate parse tree visitor (default)"),
+		new Option("genPackage",		"-package", OptionArgType.STRING, "specify a package/namespace for the generated code"),
 		new Option("",					"-D<option>=value", "set/override a grammar-level option"),
 
 

tool/src/org/antlr/v4/codegen/model/LexerFile.java

@@ -37,6 +37,7 @@ import java.util.HashMap;
 import java.util.Map;
 
 public class LexerFile extends OutputFile {
+	public String genPackage; // from -package cmd-line
 	@ModelElement public Lexer lexer;
 	@ModelElement public Map<String, Action> namedActions;
 
@@ -48,5 +49,6 @@ public class LexerFile extends OutputFile {
 			ActionAST ast = g.namedActions.get(name);
 			namedActions.put(name, new Action(factory, ast));
 		}
+		genPackage = factory.getGrammar().tool.genPackage;
 	}
 }

tool/src/org/antlr/v4/codegen/model/ParserFile.java

@@ -38,6 +38,7 @@ import java.util.Map;
 
 /** */
 public class ParserFile extends OutputFile {
+	public String genPackage; // from -package cmd-line
 	@ModelElement public Parser parser;
 	@ModelElement public Map<String, Action> namedActions;
 
@@ -49,5 +50,6 @@ public class ParserFile extends OutputFile {
 			ActionAST ast = g.namedActions.get(name);
 			namedActions.put(name, new Action(factory, ast));
 		}
+		genPackage = factory.getGrammar().tool.genPackage;
 	}
 }