├── src └── main │ ├── resources │ └── AddBetweenElements.png │ └── java │ ├── Action.java │ └── UndoRedoList.java ├── .gitignore ├── readme.md ├── test └── UndoRedoTest.java └── license /src/main/resources/AddBetweenElements.png: -------------------------------------------------------------------------------- https://raw.githubusercontent.com/Muddz/UndoRedoList/HEAD/src/main/resources/AddBetweenElements.png -------------------------------------------------------------------------------- /.gitignore: -------------------------------------------------------------------------------- 1 | .idea/ 2 | *.iml 3 | .iws 4 | out/ 5 | 6 | # Package Files # 7 | *.jar 8 | *.war 9 | *.nar 10 | *.ear 11 | *.zip 12 | *.tar.gz 13 | *.rar 14 | 15 | # Log file 16 | *.log 17 | 18 | # Java # 19 | # Compiled class file 20 | *.class 21 | 22 | 23 | 24 | -------------------------------------------------------------------------------- /src/main/java/Action.java: -------------------------------------------------------------------------------- 1 | import org.jetbrains.annotations.Nullable; 2 | 3 | public class Action { 4 | public final String key; 5 | public final Object value; 6 | 7 | public Action(String key, Object value) { 8 | this.key = key; 9 | this.value = value; 10 | } 11 | 12 | @Override 13 | public boolean equals(@Nullable Object obj) { 14 | return obj instanceof Action && 15 | ((Action) obj).key.equals(key) && 16 | ((Action) obj).value.equals(value); 17 | } 18 | } 19 | -------------------------------------------------------------------------------- /readme.md: -------------------------------------------------------------------------------- 1 | # UndoRedoList 2 | 3 | An undo-redo data structure based on the concepts of DoublyLinkedList and behaves exactly the same way as undo-redo features do in Photoshop and Microsoft Word. [Regret](https://github.com/Muddz/Regret) an Android library also uses this data structure. 4 | 5 | ## How it works 6 | 7 | The list adds nodes in sequential order as a LinkedList would do when the pointer is at the end of the list. 8 | 9 | If the pointer is on the head node or between existing nodes as shown below when adding a new entry, all nodes to the right of the pointer inclusive the node pointed at, will be replaced with the new node. 10 | 11 | 12 | 13 | Each node contains of an instance of [Action](https://github.com/Muddz/UndoRedoList/blob/master/src/main/java/Action.java) with field members: `String key` and `Object value` used for holding the key-value of an entry. 14 | 15 | To add to the UndoRedoList you call `undoRedo.add(KEY_TEXT_COLOR, Color.BLACK, Color.RED);` 16 | where `KEY_TEXT_COLOR` is used to identify the type of data and `Color.BLACK` and `Color.RED` is the old and new value. 17 | 18 | ## Performance 19 | UndoRedoList is a linear data structure and has similar performance as Java's LinkedList. 20 | The following is the *time-complexity* for the important methods in `UndoRedoList` 21 | 22 | - `add()` is always *O(1)* regardless of the pointer position 23 | - `undo()` or `redo()` is *O(1)* because we can only traverse to the next or previous node 24 | 25 | 26 | ## License 27 | 28 | Copyright 2019 Muddi Walid 29 | 30 | Licensed under the Apache License, Version 2.0 (the "License"); 31 | you may not use this file except in compliance with the License 32 | You may obtain a copy of the License at 33 | 34 | http://www.apache.org/licenses/LICENSE-2.0 35 | 36 | Unless required by applicable law or agreed to in writing, software 37 | distributed under the License is distributed on an "AS IS" BASIS, 38 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 39 | See the License for the specific language governing permissions and 40 | limitations under the License. 41 | -------------------------------------------------------------------------------- /test/UndoRedoTest.java: -------------------------------------------------------------------------------- 1 | import org.junit.jupiter.api.Assertions; 2 | import org.junit.jupiter.api.BeforeEach; 3 | import org.junit.jupiter.api.Test; 4 | 5 | import java.awt.*; 6 | 7 | public class UndoRedoTest { 8 | 9 | private static final String KEY_BACKGROUND_COLOR = "KEY_BACKGROUND_COLOR"; 10 | private static final String KEY_TEXT_COLOR = "KEY_TEXT_COLOR"; 11 | private UndoRedoList undoRedo; 12 | 13 | @BeforeEach 14 | public void setUp() { 15 | undoRedo = new UndoRedoList(); 16 | undoRedo.add(KEY_BACKGROUND_COLOR, Color.WHITE, Color.RED); 17 | undoRedo.add(KEY_BACKGROUND_COLOR, Color.RED, Color.GREEN); 18 | undoRedo.add(KEY_BACKGROUND_COLOR, Color.GREEN, Color.BLUE); 19 | } 20 | 21 | @Test 22 | public void testAddOnHead() { 23 | while (undoRedo.canUndo()) { 24 | undoRedo.undo(); 25 | } 26 | undoRedo.add(KEY_BACKGROUND_COLOR, Color.BLUE, Color.BLACK); 27 | Assertions.assertEquals(2, undoRedo.getSize()); 28 | 29 | Action action = undoRedo.getCurrent(); 30 | Assertions.assertEquals(Color.BLACK, action.value); 31 | 32 | action = undoRedo.undo(); 33 | Assertions.assertEquals(Color.BLUE, action.value); 34 | 35 | Assertions.assertFalse(undoRedo.canUndo()); 36 | undoRedo.redo(); 37 | Assertions.assertFalse(undoRedo.canRedo()); 38 | } 39 | 40 | @Test 41 | public void testAddInBetween() { 42 | undoRedo.undo(); 43 | undoRedo.add(KEY_BACKGROUND_COLOR, Color.BLUE, Color.BLACK); 44 | Assertions.assertEquals(4, undoRedo.getSize()); 45 | 46 | Action action = undoRedo.getCurrent(); 47 | Assertions.assertEquals(Color.BLACK, action.value); 48 | 49 | Assertions.assertTrue(undoRedo.canUndo()); 50 | Assertions.assertFalse(undoRedo.canRedo()); 51 | 52 | action = undoRedo.undo(); 53 | Assertions.assertEquals(Color.GREEN, action.value); 54 | 55 | action = undoRedo.undo(); 56 | Assertions.assertEquals(Color.RED, action.value); 57 | } 58 | 59 | 60 | @Test 61 | public void testUndo() { 62 | Action action = undoRedo.undo(); 63 | Assertions.assertEquals(KEY_BACKGROUND_COLOR, action.key); 64 | Assertions.assertEquals(Color.GREEN, action.value); 65 | 66 | action = undoRedo.undo(); 67 | Assertions.assertEquals(KEY_BACKGROUND_COLOR, action.key); 68 | Assertions.assertEquals(Color.RED, action.value); 69 | } 70 | 71 | @Test 72 | public void testUndoWithMixedKeys() { 73 | undoRedo.add(KEY_TEXT_COLOR, Color.BLACK, Color.RED); 74 | Action action = undoRedo.undo(); 75 | Assertions.assertEquals(KEY_TEXT_COLOR, action.key); 76 | Assertions.assertEquals(Color.BLACK, action.value); 77 | } 78 | 79 | @Test 80 | public void testRedo() { 81 | while (undoRedo.canUndo()) { 82 | undoRedo.undo(); 83 | } 84 | 85 | Action action = undoRedo.redo(); 86 | Assertions.assertEquals(KEY_BACKGROUND_COLOR, action.key); 87 | Assertions.assertEquals(Color.RED, action.value); 88 | 89 | action = undoRedo.redo(); 90 | Assertions.assertEquals(KEY_BACKGROUND_COLOR, action.key); 91 | Assertions.assertEquals(Color.GREEN, action.value); 92 | } 93 | 94 | @Test 95 | public void testRedoWithMixedKeys() { 96 | undoRedo.add(KEY_TEXT_COLOR, Color.BLACK, Color.RED); 97 | undoRedo.undo(); 98 | Action action = undoRedo.redo(); 99 | Assertions.assertEquals(KEY_TEXT_COLOR, action.key); 100 | Assertions.assertEquals(Color.RED, action.value); 101 | } 102 | 103 | @Test 104 | public void testSize() { 105 | Assertions.assertEquals(4, undoRedo.getSize()); 106 | } 107 | 108 | @Test 109 | public void testCanUndo() { 110 | Assertions.assertTrue(undoRedo.canUndo()); 111 | } 112 | 113 | @Test 114 | public void testCanNotRedo() { 115 | Assertions.assertFalse(undoRedo.canRedo()); 116 | } 117 | 118 | @Test 119 | public void testClear() { 120 | undoRedo.clear(); 121 | Assertions.assertEquals(0, undoRedo.getSize()); 122 | Assertions.assertTrue(undoRedo.isEmpty()); 123 | Assertions.assertFalse(undoRedo.canUndo()); 124 | Assertions.assertFalse(undoRedo.canRedo()); 125 | } 126 | 127 | @Test 128 | public void testGetCurrentValue() { 129 | Action action = undoRedo.getCurrent(); 130 | Assertions.assertEquals(Color.BLUE, action.value); 131 | } 132 | } -------------------------------------------------------------------------------- /src/main/java/UndoRedoList.java: -------------------------------------------------------------------------------- 1 | 2 | import org.jetbrains.annotations.NotNull; 3 | import org.jetbrains.annotations.Nullable; 4 | 5 | import java.util.ArrayList; 6 | import java.util.NoSuchElementException; 7 | 8 | /* 9 | * Copyright 2019 Muddi Walid 10 | * Licensed under the Apache License, Version 2.0 (the "License"); 11 | * you may not use this file except in compliance with the License. 12 | * You may obtain a copy of the License at 13 | * 14 | * http://www.apache.org/licenses/LICENSE-2.0 15 | * 16 | * Unless required by applicable law or agreed to in writing, software 17 | * distributed under the License is distributed on an "AS IS" BASIS, 18 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 19 | * See the License for the specific language governing permissions and 20 | * limitations under the License. 21 | */ 22 | 23 | /** 24 | * @author Muddi Walid 25 | * https://github.com/Muddz/UndoRedoList 26 | */ 27 | 28 | public class UndoRedoList { 29 | 30 | private Node head; 31 | private Node pointer; 32 | private int pointerIndex; 33 | private int size; 34 | 35 | private static class Node { 36 | Action action; 37 | Node next = null; 38 | Node prev = null; 39 | 40 | Node(Action action) { 41 | this.action = action; 42 | } 43 | } 44 | 45 | /** 46 | * Adds an key-values pair data to the collection. 47 | * Both currentValue and newValue should be of the same key identifier 48 | */ 49 | public void add(@NotNull String key, @NotNull Object currentValue, @NotNull Object newValue) { 50 | final Node oldNode = new Node(new Action(key, currentValue)); 51 | final Node newNode = new Node(new Action(key, newValue)); 52 | if (head == null || pointer == head) { 53 | oldNode.next = newNode; 54 | newNode.prev = oldNode; 55 | head = oldNode; 56 | pointerIndex = 2; 57 | } else { 58 | if (pointer.action.key.equals(key) || pointer.prev.action.key.equals(key)) { 59 | newNode.prev = pointer; 60 | pointer.next = newNode; 61 | pointerIndex++; 62 | } else { 63 | oldNode.next = newNode; 64 | newNode.prev = oldNode; 65 | pointer.next = oldNode; 66 | oldNode.prev = pointer; 67 | pointerIndex += 2; 68 | } 69 | } 70 | size = pointerIndex; 71 | pointer = newNode; 72 | } 73 | 74 | /** 75 | * @return the previous {@link Action} object without moving the pointer 76 | * @throws NoSuchElementException if the previous object doesn't exist 77 | */ 78 | public Action getPrevious() { 79 | if (pointer == null) { 80 | throw new NoSuchElementException(); 81 | } 82 | return pointer.prev.action; 83 | } 84 | 85 | /** 86 | * @return the next {@link Action} object without moving the pointer 87 | * @throws NoSuchElementException if the next object doesn't exist 88 | */ 89 | public Action getNext() { 90 | if (pointer == null) { 91 | throw new NoSuchElementException(); 92 | } 93 | return pointer.next.action; 94 | } 95 | 96 | /** 97 | * @return the current {@link Action} object which the pointer is pointing at 98 | * @throws NoSuchElementException if the current object doesn't exist because the list is empty 99 | */ 100 | public Action getCurrent() { 101 | if (pointer == null) { 102 | throw new NoSuchElementException(); 103 | } 104 | return pointer.action; 105 | } 106 | 107 | /** 108 | * Moves the pointer one step forward 109 | * 110 | * @return Returns the next {@link Action} object 111 | * @throws NoSuchElementException if the next object doesn't exist 112 | */ 113 | @Nullable 114 | public Action redo() { 115 | if (pointer.next != null) { 116 | Node tempPointer = pointer; 117 | pointer = pointer.next; 118 | pointerIndex++; 119 | if (tempPointer.action.key.equals(pointer.action.key)) { 120 | return pointer.action; 121 | } else if (pointer.next != null) { 122 | pointerIndex++; 123 | pointer = pointer.next; 124 | return pointer.action; 125 | } 126 | } 127 | throw new NoSuchElementException(); 128 | } 129 | 130 | /** 131 | * Moves the pointer one step backwards 132 | * 133 | * @return Returns the previous {@link Action} object or null if next object doesn't exists 134 | * @throws NoSuchElementException if the previous object doesn't exist 135 | */ 136 | 137 | @Nullable 138 | public Action undo() { 139 | if (pointer.prev != null) { 140 | Node tempPointer = pointer; 141 | pointer = pointer.prev; 142 | pointerIndex--; 143 | if (tempPointer.action.key.equals(pointer.action.key)) { 144 | return pointer.action; 145 | } else if (pointer.prev != null) { 146 | pointerIndex--; 147 | pointer = pointer.prev; 148 | return pointer.action; 149 | } 150 | } 151 | throw new NoSuchElementException(); 152 | } 153 | 154 | /** 155 | * @return a boolean for whether a next element exists 156 | */ 157 | public boolean canRedo() { 158 | return pointer != null && pointer.next != null; 159 | } 160 | 161 | /** 162 | * @return a boolean for whether a previous element exists 163 | */ 164 | public boolean canUndo() { 165 | return pointer != null && pointer.prev != null; 166 | } 167 | 168 | /** 169 | * @return the size of the list 170 | */ 171 | public int getSize() { 172 | return size; 173 | } 174 | 175 | /** 176 | * @return a boolean for whether the collection is empty or not 177 | */ 178 | public boolean isEmpty() { 179 | return size == 0; 180 | } 181 | 182 | /** 183 | * Deletes all elements in the collection and sets the size to 0 184 | */ 185 | public void clear() { 186 | head = null; 187 | pointer = null; 188 | size = 0; 189 | pointerIndex = 0; 190 | } 191 | 192 | /** 193 | * @return a string representation of all elements in the collection 194 | */ 195 | public String toString() { 196 | StringBuilder sb = new StringBuilder().append('{'); 197 | Node tempNode = head; 198 | while (tempNode != null) { 199 | sb.append(String.format("%s=%s", tempNode.action.key, tempNode.action.value)); 200 | tempNode = tempNode.next; 201 | if (tempNode != null) { 202 | sb.append(',').append(' '); 203 | } 204 | } 205 | return sb.append('}').toString(); 206 | } 207 | } 208 | -------------------------------------------------------------------------------- /license: -------------------------------------------------------------------------------- 1 | Apache License 2 | Version 2.0, January 2004 3 | http://www.apache.org/licenses/ 4 | 5 | TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 6 | 7 | 1. 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