Java Basics Introduction Essay (4) JavaSE Edition - Program Flow Control

The previous section had a rough understanding of the operator. This section reviews program flow control! Program flow control includes sequence structure, judgment structure (if), selection structure (switch), and loop structure.

1. Judgment structure

①The first format of if statement:

       if (conditional expression)
{
  into the ternary operator.

③The third format of if statement:

 Execution statement;

；

       }

2.选择结构

    switch(表达式)
        {
            case 取值1:
                执行语句；

                break；

            case 取值2:

                执行语句；

                break；
            …...
default:
                                                                                                                                                                                                                                            When making a selection, switch first selects the first valid choice, and if neither is true, then selects default; the switch execution structure ends when it encounters curly brackets or break, otherwise it continues to execute until the condition is true!

Special case:

             int x = 2; //break;
                                                                                                                                         out.println ("a"); :
              System.out.println("c");
break;
                                                                                                                                                                                                   ’’’ With d a b’s output d a b, principle: there is no break when executing to default, and default is placed at the front, so it will continue to execute downwards without judging other answers, and the executable statements will be executed according to the sequential structure. Until break or the end of the curly bracket is encountered, so the output order should be d a b;



application of if and switch:

if:
1. Judge the specific value.
2. Judge the interval.
3. Judge the expression whose operation result is boolean type.

switch:
1. Judge the specific value.

2. The number of values ​​is usually fixed.

For several fixed value judgments, it is recommended to use the switch statement, because the switch statement will load the specific answers into the memory.

The efficiency is relatively high.

3. Loop structure

①.while method:

 while (conditional expression)
                                                                                                                                                                                                                                                                                  Conditional expression);

Note: Characteristics of the do while statement: Regardless of whether the condition is met, the loop body is executed at least once.

③.for method:

for (initialization expression; loop condition expression; operation expression after loop)
In the running sequence, the initialization expression is read only once, the loop body is executed when the loop condition is true, and then the operation expression after the loop is executed, and then the loop condition is continued to be judged, and this process is repeated until the condition is not satisfied.

                                                                                                                                           defined for the loop's variable is released in the memory at the end of the for loop, while the variables used in the while loop can continue to be used after the end of the loop.

The simplest infinite loop format: while (true), for (;;), the reason why infinite loop exists is that we don’t know how many times it will loop, but judge the loop based on certain conditions.

4. Other flow control statements

break (jump out) statement: Scope of application: selection structure and loop structure.

continue statement: applied to loop structures.

Note: a, these two statements are meaningless outside the scope of application.

句 B, there are no sentences below these two statements, because it cannot be executed. U C, Continue statement is to end this cycle and continue the next cycle. ， D, the appearance of the label can make these two statements affect the specified range.

Example:

Example of labeling:

xiaoqiang:for (int x=0; x<3;x++)

{

System. out.println (" Net (www.php.cn)!