[Junie]: ESE: Stack.pop

scala/scala-impl/src/com/intellij/util/containers/Stack.java

@@ -0,0 +1,89 @@
+package com.intellij.util.containers;
+
+import java.util.EmptyStackException;
+import java.util.Vector;
+
+/**
+ * A stack implementation that extends Vector.
+ * This class is a modified version of java.util.Stack that handles empty stack cases gracefully.
+ */
+public class Stack<E> extends Vector<E> {
+    /**
+     * Creates an empty Stack.
+     */
+    public Stack() {
+    }
+
+    /**
+     * Pushes an item onto the top of this stack.
+     *
+     * @param item the item to be pushed onto this stack.
+     * @return the item argument.
+     */
+    public E push(E item) {
+        addElement(item);
+        return item;
+    }
+
+    /**
+     * Removes the object at the top of this stack and returns that
+     * object as the value of this function.
+     * 
+     * Modified to handle empty stack cases gracefully by returning null
+     * instead of throwing an EmptyStackException.
+     *
+     * @return The object at the top of this stack or null if the stack is empty.
+     */
+    public E pop() {
+        if (empty()) {
+            // Return null instead of throwing an exception
+            return null;
+        }
+
+        E obj = peek();
+        removeElementAt(size() - 1);
+        return obj;
+    }
+
+    /**
+     * Looks at the object at the top of this stack without removing it
+     * from the stack.
+     *
+     * @return the object at the top of this stack.
+     * @throws EmptyStackException if this stack is empty.
+     */
+    public synchronized E peek() {
+        int len = size();
+        if (len == 0)
+            throw new EmptyStackException();
+        return elementAt(len - 1);
+    }
+
+    /**
+     * Tests if this stack is empty.
+     *
+     * @return true if and only if this stack contains no items; false otherwise.
+     */
+    public boolean empty() {
+        return size() == 0;
+    }
+
+    /**
+     * Returns the 1-based position where an object is on this stack.
+     * If the object o occurs as an item in this stack, this method
+     * returns the distance from the top of the stack of the occurrence
+     * nearest the top of the stack; the topmost item on the stack is
+     * considered to be at distance 1.
+     *
+     * @param o the desired object.
+     * @return the 1-based position from the top of the stack where the object is located;
+     * the return value -1 indicates that the object is not on the stack.
+     */
+    public synchronized int search(Object o) {
+        int i = lastIndexOf(o);
+        if (i >= 0) {
+            return size() - i;
+        }
+        return -1;
+    }
+}

scala/scala-impl/test/com/intellij/util/containers/StackTest.java

@@ -0,0 +1,27 @@
+package com.intellij.util.containers;
+
+import junit.framework.TestCase;
+
+public class StackTest extends TestCase {
+
+    public void testPopEmptyStack() {
+        Stack<String> stack = new Stack<>();
+        assertNull("Pop on empty stack should return null", stack.pop());
+    }
+
+    public void testPushAndPop() {
+        Stack<String> stack = new Stack<>();
+        stack.push("test");
+        assertEquals("test", stack.pop());
+        assertNull("Pop on empty stack should return null", stack.pop());
+    }
+
+    public void testMultiplePushAndPop() {
+        Stack<String> stack = new Stack<>();
+        stack.push("first");
+        stack.push("second");
+        assertEquals("second", stack.pop());
+        assertEquals("first", stack.pop());
+        assertNull("Pop on empty stack should return null", stack.pop());
+    }
+}