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Today I was trying to push in java.util.Stack class and then use the Iterator to iterate (without using pop) through the items. I was expecting LIFO property but got surprised.
Here is the code that I was trying.
import java.util.*; import java.util.Stack; public class Main { public static void main(String[] args) { RobStack<Integer> rstack = new RobStack<Integer>(); // Correct Implementation Stack<Integer> jstack = new Stack<Integer>(); // Default Java Implementation rstack.push(0); jstack.push(0); rstack.push(1); jstack.push(1); rstack.push(2); jstack.push(2); rstack.push(3); jstack.push(3); System.out.print("Algo Stack: "); for (int i : rstack) System.out.print(i + " "); System.out.print("\nJava Stack: "); for (int i : jstack) System.out.print(i + " "); } } The output the above program is given below:
Algo Stack: 3 2 1 0 Java Stack: 0 1 2 3 In the above code jstack uses the default Java implementation and rstack uses the implementation provided by Robert Sedgewick for his Algorithm class. I found that Prof. Robert's implementation works fine but the java.util.Stack implementation fails.
Is it a bug or is it by design?
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An Iterator is an object that can be used to loop through collections, like ArrayList and HashSet. It is called an "iterator" because "iterating" is the technical term for looping. To use an Iterator, you must import it from the java. util package.
Iterator in Java is an object used to cycle through arguments or elements present in a collection. It is derived from the technical term “iterating,” which means looping through. Generally, an iterator in Java is used to loop through any collection of objects.
An iterator over a collection. Iterator takes the place of Enumeration in the Java Collections Framework. Iterators differ from enumerations in two ways: Iterators allow the caller to remove elements from the underlying collection during the iteration with well-defined semantics. Method names have been improved.
See Bug ID 4475301 : RFE: java.util.Stack.iterator() iterates the wrong way. This behavior is by (bad) design. Java's built-in Stack iterator methods are inherited from other classes, so they don't behave as you'd expect.
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