Generic (n-ary) Tree in Java

Creating the tree is pretty simple. Here is a snippet:

[sourcecode=java]
/*
We're building a tree that looks like this:

I am root!
/\
A B
/\
C D
\
E
*/

GenericTree tree = new GenericTree();

GenericTreeNode root = new GenericTreeNode("I am root!");
GenericTreeNode childA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");
GenericTreeNode childE = new GenericTreeNode("E");

childD.addChild(childE);

childB.addChild(childC);
childB.addChild(childD);

root.addChild(childA);
root.addChild(childB);

tree.setRoot(root);
[/sourcecode]

Of course, simply writing a data structure is not enough. We need tests!

TestGenericTreeNode.java

[sourcecode="java"]
import org.testng.annotations.Test;
import java.util.ArrayList;
import java.util.List;
import static org.testng.Assert.*;

public class TestGenericTreeNode {
@Test
public void TestNodeDataIsNullOnNewNodeCreation() {
GenericTreeNode node = new GenericTreeNode();
assertNull(node.getData());
}

@Test
public void TestNodeHasNonNullChildrenListOnNewNodeCreation() {
GenericTreeNode node = new GenericTreeNode();
assertNotNull(node.getChildren());
}

@Test
public void TestNodeHasZeroChildrenOnNewNodeCreation() {
GenericTreeNode node = new GenericTreeNode();
assertEquals(node.getNumberOfChildren(), 0);
}

@Test
public void TestNodeHasChildrenReturnsFalseOnNewNodeCreation() {
GenericTreeNode node = new GenericTreeNode();
assertFalse(node.hasChildren());
}

@Test
public void TestNodeDataIsNonNullWithParameterizedConstructor() {
GenericTreeNode node = new GenericTreeNode("I haz data");
assertNotNull(node.getData());
}

@Test
public void TestNodeSetAndGetData() {
GenericTreeNode node = new GenericTreeNode();
String data = "data";
node.setData(data);
assertEquals(node.getData(), data);
}

@Test
public void TestNodeSetAndGetChildren() {
GenericTreeNode node = new GenericTreeNode();
GenericTreeNode child = new GenericTreeNode();

List> children = new ArrayList>();
children.add(child);

node.setChildren(children);
assertEquals(node.getChildren(), children);
}

@Test
public void TestNodeRemoveChildren() {
GenericTreeNode node = new GenericTreeNode();
GenericTreeNode child = new GenericTreeNode();

List> children = new ArrayList>();
children.add(child);

node.setChildren(children);
node.removeChildren();
assertEquals(node.getChildren().size(), 0);
}

@Test
public void TestNodeAddChildHasOneChild() {
GenericTreeNode node = new GenericTreeNode();
GenericTreeNode child = new GenericTreeNode();

node.addChild(child);
assertEquals(node.getNumberOfChildren(), 1);
}

@Test
public void TestNodeAddChildHasChildrenIsTrue() {
GenericTreeNode node = new GenericTreeNode();
GenericTreeNode child = new GenericTreeNode();

node.addChild(child);
assertTrue(node.hasChildren());

}

@Test
public void TestNodeAddAndGetChildAt() {
GenericTreeNode node = new GenericTreeNode("root");
GenericTreeNode child1 = new GenericTreeNode("child1");
GenericTreeNode child2 = new GenericTreeNode("child2");

node.addChild(child1);
node.addChildAt(1, child2);

assertEquals(node.getChildAt(1).getData(), child2.getData());
}

@Test
public void TestNodeAddAndRemoveChildAt() {
GenericTreeNode node = new GenericTreeNode("root");
GenericTreeNode child1 = new GenericTreeNode("child1");
GenericTreeNode child2 = new GenericTreeNode("child2");

node.addChild(child1);
node.addChildAt(1, child2);

node.removeChildAt(0);

assertEquals(node.getNumberOfChildren(), 1);
}

@Test(expectedExceptions = java.lang.IndexOutOfBoundsException.class)
public void TestNodeAddChildAtThrowsException() {
GenericTreeNode node = new GenericTreeNode();
GenericTreeNode child = new GenericTreeNode();

node.addChildAt(5, child);
}

@Test(expectedExceptions = java.lang.IndexOutOfBoundsException.class)
public void TestNodeRemoveChildAtThrowsException() {
GenericTreeNode node = new GenericTreeNode();
node.removeChildAt(1);
}

@Test
public void TestNodeToString() {
GenericTreeNode node = new GenericTreeNode();
node.setData("data");
assertEquals(node.toString(), "data");
}

@Test
public void TestNodeToStringVerboseNoChildren() {
GenericTreeNode node = new GenericTreeNode();
node.setData("data");
assertEquals(node.toStringVerbose(), "data:[]");
}

@Test
public void TestNodeToStringVerboseOneChild() {
GenericTreeNode node = new GenericTreeNode();
node.setData("data");

GenericTreeNode child = new GenericTreeNode();
child.setData("child");

node.addChild(child);
assertEquals(node.toStringVerbose(), "data:[child]");
}

@Test
public void TestNodeToStringVerboseMoreThanOneChild() {
GenericTreeNode node = new GenericTreeNode();
node.setData("data");

GenericTreeNode child1 = new GenericTreeNode();
child1.setData("child1");

GenericTreeNode child2 = new GenericTreeNode();
child2.setData("child2");

node.addChild(child1);
node.addChild(child2);

assertEquals(node.toStringVerbose(), "data:[child1, child2]");
}
}
[/sourcecode]

TestGenericTree.java
[sourcecode lang="java"]
import org.testng.annotations.Test;
import java.util.*;
import static org.testng.Assert.*;

public class TestGenericTree {
@Test
public void TestRootIsNullOnNewTreeCreation() {
GenericTree tree = new GenericTree();
assertNull(tree.getRoot());
}

@Test
public void TestNumberOfNodesIsZeroOnNewTreeCreation() {
GenericTree tree = new GenericTree();
assertEquals(tree.getNumberOfNodes(), 0);
}

@Test
public void TestIsEmptyIsTrueOnNewTreeCreation() {
GenericTree tree = new GenericTree();
assertTrue(tree.isEmpty());
}

@Test
void TestExistsIsFalseOnNewTreeCreation() {
GenericTree tree = new GenericTree();
GenericTreeNode nodeToFind = new GenericTreeNode();

assertFalse(tree.exists(nodeToFind));
}

@Test
void TestFindReturnsNullOnNewTreeCreation() {
GenericTree tree = new GenericTree();
GenericTreeNode nodeToFind = new GenericTreeNode();

assertNull(tree.find(nodeToFind));
}

@Test
void TestPreOrderBuildReturnsNullListOnNewTreeCreation() {
GenericTree tree = new GenericTree();

assertNull(tree.build(GenericTreeTraversalOrderEnum.PRE_ORDER));
}

@Test
void TestPostOrderBuildReturnsNullListOnNewTreeCreation() {
GenericTree tree = new GenericTree();

assertNull(tree.build(GenericTreeTraversalOrderEnum.POST_ORDER));
}

@Test
void TestPreOrderBuildWithDepthReturnsNullMapOnNewTreeCreation() {
GenericTree tree = new GenericTree();

assertNull(tree.buildWithDepth(GenericTreeTraversalOrderEnum.PRE_ORDER));
}

@Test
void TestPostOrderBuildWithDepthReturnsNullMapOnNewTreeCreation() {
GenericTree tree = new GenericTree();

assertNull(tree.buildWithDepth(GenericTreeTraversalOrderEnum.POST_ORDER));
}

@Test
void TestToStringReturnsEmptyStringOnNewTreeCreation() {
GenericTree tree = new GenericTree();

assertEquals(tree.toString(), "");
}

@Test
void TestToStringWithDepthReturnsEmptyStringOnNewTreeCreation() {
GenericTree tree = new GenericTree();

assertEquals(tree.toStringWithDepth(), "");
}

@Test
void TestSetRootGetRoot() {
GenericTree tree = new GenericTree();
GenericTreeNode root = new GenericTreeNode();
tree.setRoot(root);

assertNotNull(tree.getRoot());
}

@Test
void TestNumberOfNodesIsOneWithNonNullRoot() {
GenericTree tree = new GenericTree();
GenericTreeNode root = new GenericTreeNode();
tree.setRoot(root);

assertEquals(tree.getNumberOfNodes(), 1);
}

@Test
void TestEmptyIsFalseWithNonNullRoot() {
GenericTree tree = new GenericTree();
GenericTreeNode root = new GenericTreeNode();
tree.setRoot(root);

assertFalse(tree.isEmpty());
}

@Test
void TestPreOrderBuildListSizeIsOneWithNonNullRoot() {
GenericTree tree = new GenericTree();
GenericTreeNode root = new GenericTreeNode("root");
tree.setRoot(root);

assertEquals(tree.build(GenericTreeTraversalOrderEnum.PRE_ORDER).size(), 1);
}

@Test
void TestPostOrderBuildListSizeIsOneWithNonNullRoot() {
GenericTree tree = new GenericTree();
GenericTreeNode root = new GenericTreeNode("root");
tree.setRoot(root);

assertEquals(tree.build(GenericTreeTraversalOrderEnum.POST_ORDER).size(), 1);
}

@Test
void TestPreOrderBuildWithDepthSizeIsOneWithNonNullRoot() {
GenericTree tree = new GenericTree();
GenericTreeNode root = new GenericTreeNode("root");
tree.setRoot(root);

assertEquals(tree.buildWithDepth(GenericTreeTraversalOrderEnum.PRE_ORDER).size(), 1);
}

@Test
void TestPostOrderBuildWithDepthSizeIsOneWithNonNullRoot() {
GenericTree tree = new GenericTree();
GenericTreeNode root = new GenericTreeNode("root");
tree.setRoot(root);

assertEquals(tree.buildWithDepth(GenericTreeTraversalOrderEnum.POST_ORDER).size(), 1);
}

/*
Tree looks like:
A
/ \
B C
\
D

For the following tests

*/
@Test
void TestNumberOfNodes() {
GenericTree tree = new GenericTree();

GenericTreeNode rootA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");

childC.addChild(childD);
rootA.addChild(childB);
rootA.addChild(childC);

tree.setRoot(rootA);

assertEquals(tree.getNumberOfNodes(), 4);
}

@Test
void TestExistsReturnsTrue() {
GenericTree tree = new GenericTree();
GenericTreeNode rootA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");

childC.addChild(childD);
rootA.addChild(childB);
rootA.addChild(childC);

tree.setRoot(rootA);

GenericTreeNode nodeToFindD = new GenericTreeNode("D");

assertTrue(tree.exists(nodeToFindD));
}

@Test
void TestFindReturnsNonNull() {
GenericTree tree = new GenericTree();

GenericTreeNode rootA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");

childC.addChild(childD);
rootA.addChild(childB);
rootA.addChild(childC);

tree.setRoot(rootA);

GenericTreeNode nodeToFindD = new GenericTreeNode("D");

assertNotNull(tree.find(nodeToFindD));
}

@Test
void TestExistsReturnsFalse() {
GenericTree tree = new GenericTree();

GenericTreeNode rootA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");

childC.addChild(childD);
rootA.addChild(childB);
rootA.addChild(childC);

tree.setRoot(rootA);

GenericTreeNode nodeToFindE = new GenericTreeNode("E");

assertFalse(tree.exists(nodeToFindE));
}

@Test
void TestFindReturnsNull() {
GenericTree tree = new GenericTree();

GenericTreeNode rootA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");

childC.addChild(childD);
rootA.addChild(childB);
rootA.addChild(childC);

tree.setRoot(rootA);

GenericTreeNode nodeToFindE = new GenericTreeNode("E");

assertNull(tree.find(nodeToFindE));
}

// Pre-order traversal will give us A B C D
@Test
void TestPreOrderBuild() {
GenericTree tree = new GenericTree();

GenericTreeNode rootA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");

childC.addChild(childD);
rootA.addChild(childB);
rootA.addChild(childC);

tree.setRoot(rootA);

List> preOrderList = new ArrayList>();
preOrderList.add(new GenericTreeNode("A"));
preOrderList.add(new GenericTreeNode("B"));
preOrderList.add(new GenericTreeNode("C"));
preOrderList.add(new GenericTreeNode("D"));

// Instead of checking equalities on the lists themselves, we can check equality on the toString's
// they should generate the same toString's

assertEquals(tree.build(GenericTreeTraversalOrderEnum.PRE_ORDER).toString(), preOrderList.toString());
}

//Post-order traversal will give us B D C A
@Test
void TestPostOrderBuild() {
GenericTree tree = new GenericTree();

GenericTreeNode rootA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");

childC.addChild(childD);
rootA.addChild(childB);
rootA.addChild(childC);

tree.setRoot(rootA);

List> postOrderList = new ArrayList>();
postOrderList.add(new GenericTreeNode("B"));
postOrderList.add(new GenericTreeNode("D"));
postOrderList.add(new GenericTreeNode("C"));
postOrderList.add(new GenericTreeNode("A"));

// Instead of checking equalities on the lists themselves, we can check equality on the toString's
// they should generate the same toString's

assertEquals(tree.build(GenericTreeTraversalOrderEnum.POST_ORDER).toString(), postOrderList.toString());
}

//Pre-order traversal with depth will give us A:0, B:1, C:1, D:2
@Test
void TestPreOrderBuildWithDepth() {
GenericTree tree = new GenericTree();

GenericTreeNode rootA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");

childC.addChild(childD);
rootA.addChild(childB);
rootA.addChild(childC);

tree.setRoot(rootA);

Map, Integer> preOrderMapWithDepth = new LinkedHashMap, Integer>();
preOrderMapWithDepth.put(new GenericTreeNode("A"), 0);
preOrderMapWithDepth.put(new GenericTreeNode("B"), 1);
preOrderMapWithDepth.put(new GenericTreeNode("C"), 1);
preOrderMapWithDepth.put(new GenericTreeNode("D"), 2);

// Instead of checking equalities on the maps themselves, we can check equality on the toString's
// they should generate the same toString's

assertEquals(tree.buildWithDepth(GenericTreeTraversalOrderEnum.PRE_ORDER).toString(), preOrderMapWithDepth.toString());
}

//Post-order traversal with depth will give us B:1, D:2, C:1, A:0
@Test
void TestPostOrderBuildWithDepth() {
GenericTree tree = new GenericTree();

GenericTreeNode rootA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");

childC.addChild(childD);
rootA.addChild(childB);
rootA.addChild(childC);

tree.setRoot(rootA);

Map, Integer> postOrderMapWithDepth = new LinkedHashMap, Integer>();
postOrderMapWithDepth.put(new GenericTreeNode("B"), 1);
postOrderMapWithDepth.put(new GenericTreeNode("D"), 2);
postOrderMapWithDepth.put(new GenericTreeNode("C"), 1);
postOrderMapWithDepth.put(new GenericTreeNode("A"), 0);

// Instead of checking equalities on the maps themselves, we can check equality on the toString's
// they should generate the same toString's

assertEquals(tree.buildWithDepth(GenericTreeTraversalOrderEnum.POST_ORDER).toString(), postOrderMapWithDepth.toString());
}

//toString and toStringWithDepth both use pre-order traversal
@Test
void TestToString() {
GenericTree tree = new GenericTree();

GenericTreeNode rootA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");

childC.addChild(childD);
rootA.addChild(childB);
rootA.addChild(childC);

tree.setRoot(rootA);

List> preOrderList = new ArrayList>();
preOrderList.add(new GenericTreeNode("A"));
preOrderList.add(new GenericTreeNode("B"));
preOrderList.add(new GenericTreeNode("C"));
preOrderList.add(new GenericTreeNode("D"));

assertEquals(tree.toString(), preOrderList.toString());
}

@Test
void TestToStringWithDepth() {
GenericTree tree = new GenericTree();

GenericTreeNode rootA = new GenericTreeNode("A");
GenericTreeNode childB = new GenericTreeNode("B");
GenericTreeNode childC = new GenericTreeNode("C");
GenericTreeNode childD = new GenericTreeNode("D");

childC.addChild(childD);
rootA.addChild(childB);
rootA.addChild(childC);

tree.setRoot(rootA);

Map, Integer> preOrderMapWithDepth = new LinkedHashMap, Integer>();
preOrderMapWithDepth.put(new GenericTreeNode("A"), 0);
preOrderMapWithDepth.put(new GenericTreeNode("B"), 1);
preOrderMapWithDepth.put(new GenericTreeNode("C"), 1);
preOrderMapWithDepth.put(new GenericTreeNode("D"), 2);

assertEquals(tree.toStringWithDepth(), preOrderMapWithDepth.toString());
}
}
[/sourcecode]

That's pretty much it. Hope you found this useful!