fix GenericStack.pop() and modify toString()

r3gor · web-flow · commit 624527324fd2 · 2020-03-02T01:59:34.000-05:00
1. Call list[size] should return null (if list[size-1] is the last element of the stack), this does not happen because the pop() method does not actually eliminate any element.

2. When pop() is called, size should never be left with a negative value.
diff --git a/Exercise_19/Exercise_19_01/GenericStack.java b/Exercise_19/Exercise_19_01/GenericStack.java
@@ -22,7 +22,12 @@ public void push(E o) {
 
 	/** Return and remove the top element from the stack */
 	public E pop() {
-		E o = list[--size];
+		if (--size < 0)
+		    size = 0;
+		E o = list[size];
+		E[] new_list = (E[]) new Object[list.length];
+		System.arraycopy(list, 0, new_list, 0, size);
+		list = new_list;
 		return o;
 	}
 
@@ -41,6 +46,15 @@ private void doubleList() {
 
 	@Override // Override the toString array in the Object class
 	public String toString() {
-		return "stack: " + list.toString();
+		String s = "Stack: [";
+		if (isEmpty())
+			return s + "]";
+		for (int i = 0; i < size; i++) {
+		    if (i == size-1)
+			s += list[i].toString() + "]";
+		    else 
+			s += list[i].toString() + ", ";
+		}
+		return s;
 	}
-}
+}
