Java theoretical basis - stack (summary sharing)

This article brings you the relevant knowledge of java, which mainly introduces the related issues about the stack, including the basic operations of the stack, the methods and properties of the stack, and the two implementations of the stack. Methods, etc., hope it helps everyone.

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1. The concept of stack

Stack (stack), also known as stack, as a data structure, is a special linear table that can only perform insertion and deletion operations at one end. It is a linear table with limited operations. The restriction is that insertion and deletion operations are only allowed at one end of the table. This end is called the top of the stack, and the other end is called the bottom. The stack has a first-in-last-out feature.

2. Basic operations of the stack

Building a stack: Before using the stack, first build an empty stack
Stack, push : Add new elements to the stack
Pop : Delete the element on the top of the stack
Read the stack : Query the element on the top of the current stack
Get the size of the stack and clear the stack. . .

3. Stack methods and attributes

##Push is for pushing into the stack

Pop is for popping out Stack

4. Two implementation methods of stack

① Array (sequence list)

The array must have a fixed length (number of elements) defined in advance

② Linked list

The linked list can be seen as consisting of small rooms. Each room relies on a pointer to point to the next room. It is The linked list linked by pointers is a non-continuous and non-sequential storage structure on the physical storage unit. The logical order of the data elements is realized through the pointer address of the linked list. Each element contains two nodes, one is to store the data of the element. field (memory space), and the other is a pointer field pointing to the next node address. Depending on the pointer pointing, the linked list can form different structures, such as singly linked list, doubly linked list, circular linked list, etc.

5. The difference between arrays and linked lists

array

Advantages:

1. Querying elements by index is fast

2. Traversing arrays by index is convenient

Disadvantages:

1. Define fixed in advance Length (number of elements)

2, cannot adapt to the dynamic increase and decrease of data.

When the data increases, it may exceed the originally defined number of elements, causing the array to go out of bounds;
When the data decreases, it causes a waste of memory.

Linked list

Advantages:

1. There is no need to initialize the capacity, and you can add or subtract elements at will;

2. When adding or deleting elements, you only need to change the pointer fields of the two element nodes before and after to point to the address, so adding and deleting are fast.

Disadvantages:

1. Because it contains a large number of pointer fields, it takes up a lot of space; finding elements requires traversing the linked list, which is very time-consuming.

For those who want to access data quickly, when inserting and deleting elements are infrequent, the selection array data volume is small, and frequent addition and deletion operations are required

And for the scenario when accessing elements If there are no high efficiency requirements, choose linked list

6. The role of the stack

6.1. Save local variables:

Local variables may also be used in functions , instead of always using global variables. Then where is the appropriate place to store local variables? That is, there should be no conflict when functions are nested, and efficiency should be focused on.

6.2 Parameter passing

The purpose of passing parameters is to reuse the code so that one method can be applied to more situations without having to write N sets of similar methods for N situations. code. So what method is used to transfer parameters? You can choose:

6.3 Save the value of the register

If there is a conflict in the parameter passed by the register, you can temporarily push the value of the register into the stack

6.4 Other functions

1) The stack is the basis of each function architecture, enabling the reuse of functions.

2) When a problem occurs, you can use the stack to understand the situation where the problem occurred.

3) The stack is the basis for building the multi-tasking mode of the operating system.

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