diff --git a/src/main/java/com/thealgorithms/datastructures/stacks/StackArray.java b/src/main/java/com/thealgorithms/datastructures/stacks/StackArray.java
index f98db7cc1..9369b3fc9 100644
--- a/src/main/java/com/thealgorithms/datastructures/stacks/StackArray.java
+++ b/src/main/java/com/thealgorithms/datastructures/stacks/StackArray.java
@@ -1,7 +1,13 @@
package com.thealgorithms.datastructures.stacks;
/**
- * This class implements a Stack using a regular array.
+ * Implements a generic stack using an array.
+ *
+ *
This stack automatically resizes when necessary, growing to accommodate additional elements and
+ * shrinking to conserve memory when its size significantly decreases.
+ *
+ *
Elements are pushed and popped in LIFO (last-in, first-out) order, where the last element added
+ * is the first to be removed.
*
* @param the type of elements in this stack
*/
@@ -13,11 +19,20 @@ public class StackArray implements Stack {
private T[] stackArray;
private int top;
+ /**
+ * Creates a stack with a default capacity.
+ */
@SuppressWarnings("unchecked")
public StackArray() {
this(DEFAULT_CAPACITY);
}
+ /**
+ * Creates a stack with a specified initial capacity.
+ *
+ * @param size the initial capacity of the stack, must be greater than 0
+ * @throws IllegalArgumentException if size is less than or equal to 0
+ */
@SuppressWarnings("unchecked")
public StackArray(int size) {
if (size <= 0) {
@@ -28,6 +43,11 @@ public class StackArray implements Stack {
this.top = -1;
}
+ /**
+ * Pushes an element onto the top of the stack. Resizes the stack if it is full.
+ *
+ * @param value the element to push
+ */
@Override
public void push(T value) {
if (isFull()) {
@@ -36,6 +56,13 @@ public class StackArray implements Stack {
stackArray[++top] = value;
}
+ /**
+ * Removes and returns the element from the top of the stack. Shrinks the stack if
+ * its size is below a quarter of its capacity, but not below the default capacity.
+ *
+ * @return the element removed from the top of the stack
+ * @throws IllegalStateException if the stack is empty
+ */
@Override
public T pop() {
if (isEmpty()) {
@@ -48,6 +75,12 @@ public class StackArray implements Stack {
return value;
}
+ /**
+ * Returns the element at the top of the stack without removing it.
+ *
+ * @return the top element of the stack
+ * @throws IllegalStateException if the stack is empty
+ */
@Override
public T peek() {
if (isEmpty()) {
@@ -56,6 +89,11 @@ public class StackArray implements Stack {
return stackArray[top];
}
+ /**
+ * Resizes the internal array to a new capacity.
+ *
+ * @param newSize the new size of the stack array
+ */
private void resize(int newSize) {
@SuppressWarnings("unchecked") T[] newArray = (T[]) new Object[newSize];
System.arraycopy(stackArray, 0, newArray, 0, top + 1);
@@ -63,21 +101,60 @@ public class StackArray implements Stack {
maxSize = newSize;
}
+ /**
+ * Checks if the stack is full.
+ *
+ * @return true if the stack is full, false otherwise
+ */
public boolean isFull() {
return top + 1 == maxSize;
}
+ /**
+ * Checks if the stack is empty.
+ *
+ * @return true if the stack is empty, false otherwise
+ */
@Override
public boolean isEmpty() {
return top == -1;
}
- @Override public void makeEmpty() { // Doesn't delete elements in the array but if you call
- top = -1; // push method after calling makeEmpty it will overwrite previous values
+ /**
+ * Empties the stack, marking it as empty without deleting elements. Elements are
+ * overwritten on subsequent pushes.
+ */
+ @Override
+ public void makeEmpty() {
+ top = -1;
}
+ /**
+ * Returns the number of elements currently in the stack.
+ *
+ * @return the size of the stack
+ */
@Override
public int size() {
return top + 1;
}
+
+ /**
+ * Returns a string representation of the stack.
+ *
+ * @return a string representation of the stack
+ */
+ @Override
+ public String toString() {
+ StringBuilder sb = new StringBuilder();
+ sb.append("StackArray [");
+ for (int i = 0; i <= top; i++) {
+ sb.append(stackArray[i]);
+ if (i < top) {
+ sb.append(", ");
+ }
+ }
+ sb.append("]");
+ return sb.toString();
+ }
}
diff --git a/src/test/java/com/thealgorithms/datastructures/stacks/StackArrayTest.java b/src/test/java/com/thealgorithms/datastructures/stacks/StackArrayTest.java
index 3cda2f547..74de7ad64 100644
--- a/src/test/java/com/thealgorithms/datastructures/stacks/StackArrayTest.java
+++ b/src/test/java/com/thealgorithms/datastructures/stacks/StackArrayTest.java
@@ -21,11 +21,11 @@ class StackArrayTest {
stack.push(4);
stack.push(5);
- Assertions.assertEquals(5, stack.pop()); // Stack follows LIFO, so 5 should be popped first
- Assertions.assertEquals(4, stack.pop()); // Next, 4 should be popped
- Assertions.assertEquals(3, stack.pop()); // Followed by 3
- Assertions.assertEquals(2, stack.pop()); // Then 2
- Assertions.assertEquals(1, stack.pop()); // Finally 1
+ Assertions.assertEquals(5, stack.pop());
+ Assertions.assertEquals(4, stack.pop());
+ Assertions.assertEquals(3, stack.pop());
+ Assertions.assertEquals(2, stack.pop());
+ Assertions.assertEquals(1, stack.pop());
}
@Test
@@ -34,34 +34,34 @@ class StackArrayTest {
stack.push(20);
stack.push(30);
- Assertions.assertEquals(30, stack.peek()); // Peek should return 30, the top of the stack
- Assertions.assertEquals(3, stack.size()); // Size should remain 3 after peek
+ Assertions.assertEquals(30, stack.peek());
+ Assertions.assertEquals(3, stack.size());
stack.pop();
- Assertions.assertEquals(20, stack.peek()); // After popping, peek should return 20
+ Assertions.assertEquals(20, stack.peek());
}
@Test
void testIsEmpty() {
- Assertions.assertTrue(stack.isEmpty()); // Initially, the stack should be empty
+ Assertions.assertTrue(stack.isEmpty());
stack.push(42);
- Assertions.assertFalse(stack.isEmpty()); // After pushing an element, the stack should not be empty
+ Assertions.assertFalse(stack.isEmpty());
stack.pop();
- Assertions.assertTrue(stack.isEmpty()); // After popping the only element, the stack should be empty again
+ Assertions.assertTrue(stack.isEmpty());
}
@Test
void testResizeOnPush() {
- StackArray smallStack = new StackArray<>(2); // Start with a small stack size
+ StackArray smallStack = new StackArray<>(2);
smallStack.push(1);
smallStack.push(2);
- Assertions.assertTrue(smallStack.isFull()); // Initially, the stack should be full
+ Assertions.assertTrue(smallStack.isFull());
- smallStack.push(3); // This push should trigger a resize
- Assertions.assertFalse(smallStack.isFull()); // The stack should no longer be full after resize
- Assertions.assertEquals(3, smallStack.size()); // Size should be 3 after pushing 3 elements
+ smallStack.push(3);
+ Assertions.assertFalse(smallStack.isFull());
+ Assertions.assertEquals(3, smallStack.size());
- Assertions.assertEquals(3, smallStack.pop()); // LIFO behavior check
+ Assertions.assertEquals(3, smallStack.pop());
Assertions.assertEquals(2, smallStack.pop());
Assertions.assertEquals(1, smallStack.pop());
}
@@ -74,13 +74,13 @@ class StackArrayTest {
stack.push(3);
stack.push(4);
- stack.pop(); // Removing elements should trigger a resize when less than 1/4 of the stack is used
stack.pop();
stack.pop();
- Assertions.assertEquals(1, stack.size()); // After popping, only one element should remain
+ stack.pop();
+ Assertions.assertEquals(1, stack.size());
stack.pop();
- Assertions.assertTrue(stack.isEmpty()); // The stack should be empty now
+ Assertions.assertTrue(stack.isEmpty());
}
@Test
@@ -90,32 +90,40 @@ class StackArrayTest {
stack.push(3);
stack.makeEmpty();
- Assertions.assertTrue(stack.isEmpty()); // The stack should be empty after calling makeEmpty
- Assertions.assertThrows(IllegalStateException.class, stack::pop); // Popping from empty stack should throw exception
+ Assertions.assertTrue(stack.isEmpty());
+ Assertions.assertThrows(IllegalStateException.class, stack::pop);
}
@Test
void testPopEmptyStackThrowsException() {
- Assertions.assertThrows(IllegalStateException.class, stack::pop); // Popping from an empty stack should throw an exception
+ Assertions.assertThrows(IllegalStateException.class, stack::pop);
}
@Test
void testPeekEmptyStackThrowsException() {
- Assertions.assertThrows(IllegalStateException.class, stack::peek); // Peeking into an empty stack should throw an exception
+ Assertions.assertThrows(IllegalStateException.class, stack::peek);
}
@Test
void testConstructorWithInvalidSizeThrowsException() {
- Assertions.assertThrows(IllegalArgumentException.class, () -> new StackArray<>(0)); // Size 0 is invalid
- Assertions.assertThrows(IllegalArgumentException.class, () -> new StackArray<>(-5)); // Negative size is invalid
+ Assertions.assertThrows(IllegalArgumentException.class, () -> new StackArray<>(0));
+ Assertions.assertThrows(IllegalArgumentException.class, () -> new StackArray<>(-5));
}
@Test
void testDefaultConstructor() {
- StackArray defaultStack = new StackArray<>(); // Using default constructor
- Assertions.assertEquals(0, defaultStack.size()); // Initially, size should be 0
+ StackArray defaultStack = new StackArray<>();
+ Assertions.assertEquals(0, defaultStack.size());
defaultStack.push(1);
- Assertions.assertEquals(1, defaultStack.size()); // After pushing, size should be 1
+ Assertions.assertEquals(1, defaultStack.size());
+ }
+
+ @Test
+ void testToString() {
+ stack.push(1);
+ stack.push(2);
+ stack.push(3);
+ Assertions.assertEquals("StackArray [1, 2, 3]", stack.toString());
}
}