Stack Assignment

Motivation

We will build three implementations of a Stack. One non-thread safe implementation, one thread-safe implementation using synchronized methods, and finally one thread-safe implementation using atomics.

Background

Node and Stack Interfaces

interface Node

public interface Node<E> {
	E value();
	Optional<Node<E>> nextNode();
}

interface Stack

public interface Stack<E> {
	void push(E value);
	Optional<E> peek();
	Optional<E> pop();
}

Example

empty

Stack<String> stack = new NotThreadSafeStack<>();

In this state, stack.peek() will return Optional.empty() and stack.pop() will also return Optional.empty().

push A, B, C, D, E

Stack<String> stack = new NotThreadSafeStack<>();
stack.push("A");
stack.push("B");
stack.push("C");
stack.push("D");
stack.push("E");

In this state, stack.peek() will return Optional.of("E").

push A, B, C, D, E, pop

Stack<String> stack = new NotThreadSafeStack<>();
stack.push("A");
stack.push("B");
stack.push("C");
stack.push("D");
stack.push("E");
Optional<String> optOfE = stack.pop();

In this state, optOfE will hold Optional.of("E") and stack.peek() will return Optional.of("D").

Code To Implement

Node

public interface Node<E> {
	E value();

	Optional<Node<E>> nextNode();
}

DefaultNode

The mighty cons cell goes back to the early days of computing. People have been building amazing systems with this data structure since the 1950s.

We will build an @Immutable class DefaultNode which implements interface Node.

class:	DefaultNode.java
methods:	value nextNode
package:	stack.node.exercise
source folder:	main/src/main/java

constructor and instance variables

The constructor

public DefaultNode(E value, Optional<Node<E>> nextNode)

is passed a value and a nextNode. Hang on to this data in instance variables. As instances of DefaultNode are to be immutable, the instance variables should be marked as final.

value

return the value.

nextNode

return the next node.

Stack

public interface Stack<E> {
	void push(E value);

	Optional<E> peek();

	Optional<E> pop();
}

NotThreadSafeStack

@NotThreadSafe

class:	NotThreadSafeStack.java
methods:	push peek pop
package:	stack.notthreadsafe.exercise
source folder:	student/src/main/java

instance variables

What state do you need to keep track of to support a mutable non-thread-safe Stack?

Distasters To Investigate

ParallelPushStackDisasterClient

class:	ParallelPushStackDisasterClient.java	DEMO:
methods:	main
package:	stack.notthreadsafe.disaster
source folder:	src/main/java

ParallelPushAndPopStackDisasterClient

class:	ParallelPushAndPopStackDisasterClient.java	DEMO:
methods:	main
package:	stack.notthreadsafe.disaster
source folder:	src/main/java

Testing

class:	StackTestSuite.java
package:	stack.exercise
source folder:	testing/src/test/java

DefaultNode

class:	_DefaultNodeTestSuite.java
package:	stack.node.exercise
source folder:	testing/src/test/java

NotThreadSafeStack

class:	_NotThreadSafeStackTestSuite.java
package:	stack.notthreadsafe.exercise
source folder:	testing/src/test/java

Pledge, Acknowledgments, Citations

file:

atomic-stack-pledge-acknowledgments-citations.txt

More info about the Honor Pledge