Data Structures

1. Data Structures • Data structures permit the storage of related data for use in your program. • Arrays

2. Data Structures • Dynamic data structures hold an unknown number of elements. • Arrays hold a specified number of elements. • Generic type data structures hold data elements of different data types. • Arrays hold data of the same data type.

3. Data Structures • Types of dynamic generic data structures are: • Stacks, queues, lists, trees

4. Stacks • What is a stack?

5. Stacks • A stack is similar in concept to a pile of plates, books, blocks, boxes, etc. • The first item put on the stack is on the bottom of the stack. • All items added to the stack are placed on top of the previous item. • The last item put on the stack is on the top of the stack.

6. Stacks • Stacks are called Last-in First-out (LIFO) data structures. • The last plate put on the top of the stack is the first plate removed from the stack. • The first plate put on the top of the stack is the last plate removed from the stack.

7. Stacks • Characteristics of stacks: • Data can only be placed on the top of the stack. • Data can only be removed from the top of the stack. • Data can only be removed from the bottom of the stack if there is only one item on the stack. • Data can not be removed from the middle of the stack without first removing all items from the top.

8. Stack Example Create a stack with the following information: • Place the following numbers in a stack in this order: 5, 8, 10, 2, 4, 12 • Remove number 10 from the stack. • Put 3, 7, 1 on the stack. • Now remove 5 from the bottom of the stack and put it on the top of the stack.

9. Stack Behaviors • The behavior of putting an item on the stack is called push. • Push 4 onto the stack. • The behavior of removing and item from the stack is called pop. • Pop 4 from the stack.

10. Example • What stack exists after executing the following commands? • push(3) • push(6) • push(8) • push(1) • pop() • pop() • push(14)

11. Stack Implementation • The ability to use a stack is not built into Java like arrays. • You can implement a stack using a list, a queue, or an array.

12. Stack Implementation • A stack class can be written using arrays that will simulate a stack in your programs. • A restriction of using arrays to implement a stack is that the total size of the stack is limited. • Why? • Can you define a method that will resize the array to hold a stack of any size?

13. Stack Implementation • Create a Stack class to hold strings. • Assume that the first element of the array is the bottom element on the stack. • How do we know the number of items on the stack? • How do we know if there is anything in the stack?

14. Stack Implementation • How do we store data of any type into our stack?

15. Object Class • Every class in Java is a child of the Object class. • The Object class is the most generic class in Java. • Therefore, we should be able to create a stack of type Object to store any data into the stack. • This is not necessarily true. Primitive data types are not descendents of type Object.

16. Type Wrapper Classes • Each primitive data type has a Type Wrapper class. • The type wrapper class for: • double is Double, • int is Integer, • float is Float, • boolean is Boolean.

17. Type Wrapper Classes • Type wrapper classes allow you to manipulate primitive data types as objects of class Object. • The type wrapper class contains functions that manipulate the data as a class.

18. Type Wrapper Classes • The primitive data type is not automatically a type wrapper version of the data type. • To define a version of the primitive data type as a type wrapper you need to create a new instance of the type wrapper. Integer newInteger = new Integer(98); Double newDouble = new Double(986.3);

19. Stack Implementation • How do we redefine our Stack class to hold data of any data type?