English Version of Java Study - Lesson 1

I. Process Control - Selection Structure

　A. Process Control Structure

　　1. Introduction to the process signs

　　　 Process begins / ends       Judge and branch

 

　　　 Calculation procedure.     Connection

 

　　　 Input / output instructions        Process line

　　2. Introduction of Process Control Structure

 

 

 　 　Sequence　　　　　　　　　 Selection　　　　　　　　   　　　Loop

　　　　a. Sequential structure: Sequential structure refers to the structure in which the program 　　　　　executes each statement in turn from top to bottom without any judgment or jumping. 　　　　　The preceding examples all adopt sequential structure.

　　　　b. Choose structure: Choose structure to execute different code according to the result of 　　　　　condition judgment. The selected structure can be subdivided into single-branch 　　　　　structure, double-branch structure and multi-branch structure. Java provides if control 　　　　　statements and switch statements to implement the selection structure.

　　　　c. Loop structure: Loop structure is to execute a piece of code repeatedly according to 　　　　　the judgment condition. Java provides while statement, DO-WHILE statement, for 　　　　　statement to implement loop structure.

　B. Selection Structure

　　1. "If"

　　　a. There are three different kinds of "If" control statement. 

　　　　- Single branch structure 

　　　　- Double branch structure

　　　　- Muti-molecular structure

　　　b. Using "If" for single branch structure

　　　　- Format: 

　　　　　　

　　　c. Steps of Judge the result of the expression:

　　　　- Judge the expressed results.

　　　　- Execute the statement if the result of the expression is true.

　　　　- If the result of the expression is false, skip the statement.

　　2. "If-else"

　　　a. Format:

　　　　　

　　　b. Steps of Judge the result of the expression:

　　　　- Judge the result of the expression

　　　　- If the result of the expression is true, execute statement 1

　　　　- If the result of the expression is false, execute statement 2

　　3. Using multi-branch if statement to realize multi-branch processing

　　　a. The grammatical format of the multi-branch if statement:

　　　　　　

　　　b. The execution steps of the multi-branch if statement:

　　　　- The result of expression 1 is judged.

　　　　- If the result of expression 1 is true, statement 1 is executed; otherwise expression 2 is judged.

　　　　- If the result of expression 2 is true, statement 2 is executed; otherwise statement 3 is executed.

　C. "Switch"

　　1. Format: 

　　　

　　2. The execution steps of the switch statement:

　　　- Calculate the value of the expression after switch

　　　- Comparing the calculated results from top to bottom with the constant values after case

　　　- If equal, the code block after the constant is executed and the break statement ends.

　　　- If the constants after any case do not match, execute the statement in default

NOTE:

01. If you need to jump out after each case is executed, don't forget to write a break after each case.

02. Constants after case cannot be the same

03. The order of default blocks can be changed, but attention should be paid to their execution order. Normally, default blocks are placed at the end, or they can be omitted.