refine getChildren() method to narrow return type.

runtime/Java/src/org/antlr/v4/runtime/RuleContext.java

@@ -34,12 +34,11 @@ import org.antlr.v4.runtime.misc.Nullable;
 import org.antlr.v4.runtime.tree.ParseTree;
 import org.antlr.v4.runtime.tree.ParseTreeVisitor;
 import org.antlr.v4.runtime.tree.RuleNode;
-import org.antlr.v4.runtime.tree.Tree;
 import org.antlr.v4.runtime.tree.Trees;
 import org.antlr.v4.runtime.tree.gui.TreeViewer;
 
 import javax.print.PrintException;
-import javax.swing.JDialog;
+import javax.swing.*;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.List;
@@ -152,7 +151,7 @@ public class RuleContext implements RuleNode {
 	}
 
 	@Override
-	public List<? extends Tree> getChildren() {
+	public List<? extends ParseTree> getChildren() {
 		return null;
 	}
 

runtime/Java/src/org/antlr/v4/runtime/tree/ParseTree.java

@@ -34,6 +34,8 @@ import org.antlr.v4.runtime.Parser;
 import org.antlr.v4.runtime.RuleContext;
 import org.antlr.v4.runtime.Token;
 
+import java.util.List;
+
 /** An interface to access the tree of {@link RuleContext} objects created
  *  during a parse that makes the data structure look like a simple parse tree.
  *  This node represents both internal nodes, rule invocations,
@@ -48,6 +50,11 @@ public interface ParseTree extends SyntaxTree {
 	@Override
 	ParseTree getChild(int i);
 
+	/** Return ordered list of all children of this node; redefine to
+	 *  refine type.
+	 */
+	List<? extends ParseTree> getChildren();
+
 	/** The {@link ParseTreeVisitor} needs a double dispatch method. */
 	public <T> T accept(ParseTreeVisitor<? extends T> visitor);
 

runtime/Java/src/org/antlr/v4/runtime/tree/TerminalNodeImpl.java

@@ -66,7 +66,7 @@ public class TerminalNodeImpl implements TerminalNode {
 	public int getChildCount() { return 0; }
 
 	@Override
-	public List<? extends Tree> getChildren() {
+	public List<? extends ParseTree> getChildren() {
 		return null;
 	}