Typify internal list in DirectGraphLayout and convert to Deque

By using a deque, we have access to both an iterator() and an
descendingIterator() method. This allows us to iterate over the
collection in both directions.

org.eclipse.draw2d.tests/src/org/eclipse/draw2d/test/LocalOptimizerTest.java

@@ -12,7 +12,8 @@
 package org.eclipse.draw2d.test;
 
 import java.lang.reflect.Field;
-import java.util.ArrayList;
+import java.util.ArrayDeque;
+import java.util.Deque;
 
 import org.eclipse.draw2d.graph.DirectedGraph;
 import org.eclipse.draw2d.graph.DirectedGraphLayout;
@@ -146,10 +147,9 @@ private static DirectedGraphLayout createDirectedGraphLayoutWithSelectedStepOnly
  DirectedGraphLayout layout = new DirectedGraphLayout();
  Field stepsField = DirectedGraphLayout.class.getDeclaredField("steps"); //$NON-NLS-1$
  stepsField.setAccessible(true);
- ArrayList steps = (ArrayList) stepsField.get(layout);
- ArrayList filteredSteps = new ArrayList();
- for (int i = 0; i < steps.size(); i++) {
- Object graphVisitor = steps.get(i);
+ Deque<?> steps = (Deque<?>) stepsField.get(layout);
+ Deque<Object> filteredSteps = new ArrayDeque<>();
+ for (Object graphVisitor : steps) {
  for (String graphVisitorClassName : graphVisitorClassNames) {
  if (graphVisitorClassName.equals(graphVisitor.getClass().getName())) {
  filteredSteps.add(graphVisitor);

org.eclipse.draw2d/src/org/eclipse/draw2d/graph/DirectedGraphLayout.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2003, 2010 IBM Corporation and others.
+ * Copyright (c) 2003, 2023 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -10,8 +10,8 @@
  *******************************************************************************/
 package org.eclipse.draw2d.graph;
 
-import java.util.ArrayList;
-import java.util.List;
+import java.util.ArrayDeque;
+import java.util.Deque;
 
 /**
  * Performs a graph layout of a <code>DirectedGraph</code>. The directed graph
@@ -70,7 +70,7 @@
  */
 public class DirectedGraphLayout {
 
- List steps = new ArrayList();
+ Deque<GraphVisitor> steps = new ArrayDeque<>();
 
  /**
  * @since 3.1
@@ -101,14 +101,8 @@ void init() {
  public void visit(DirectedGraph graph) {
  if (graph.nodes.isEmpty())
  return;
- for (int i = 0; i < steps.size(); i++) {
- GraphVisitor visitor = (GraphVisitor) steps.get(i);
- visitor.visit(graph);
- }
- for (int i = steps.size() - 1; i >= 0; i--) {
- GraphVisitor visitor = (GraphVisitor) steps.get(i);
- visitor.revisit(graph);
- }
+ steps.iterator().forEachRemaining(visitor -> visitor.visit(graph));
+ steps.descendingIterator().forEachRemaining(visitor -> visitor.revisit(graph));
  }
 
 }

org.eclipse.zest.layouts/src/org/eclipse/zest/layouts/algorithms/DirectedGraphLayoutAlgorithm.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright 2005, CHISEL Group, University of Victoria, Victoria, BC, Canada.
+ * Copyright 2005, 2023, CHISEL Group, University of Victoria, Victoria, BC, Canada.
  * All rights reserved. This program and the accompanying materials are made
  * available under the terms of the Eclipse Public License v1.0 which
  * accompanies this distribution, and is available at
@@ -10,9 +10,9 @@
 package org.eclipse.zest.layouts.algorithms;
 
 import java.lang.reflect.Field;
+import java.util.Deque;
 import java.util.HashMap;
 import java.util.Iterator;
-import java.util.List;
 
 import org.eclipse.draw2d.geometry.Dimension;
 import org.eclipse.draw2d.graph.DirectedGraph;
@@ -34,7 +34,7 @@ public void visit(DirectedGraph graph) {
  field = DirectedGraphLayout.class.getDeclaredField("steps");
  field.setAccessible(true);
  Object object = field.get(this);
- List steps = (List) object;
+ Deque<?> steps = (Deque<?>) object;
  steps.remove(10);
  steps.remove(9);
  steps.remove(8);