Java's basic grammar (IV): Statement

8. Statement

(1) The flow control statements

Classification:  sequential structure, selection structure, a cyclic structure

① sequential structure: from top to bottom, are sequentially performed

② Select structure:. IF statements and switch statements

if statement:
 
Format 1: 
if (Comparative expression) { 
  statement body;   
} 
Process: 
judgment comparison value of the expression, true body statement is executed, false not performed 

Format 2: 
if (Comparative Expression 1) { 
  statement 1;   
} the else { 
  statement 2;         
} 
process: 
determination value comparison expression 1, true statement is executed body 1, false statement 2 is executed 

format. 3: 
IF (Comparative expression 1) { 
  statement body 1;   
} the else  IF ( Comparative expression 2) { 
  statement body 2;         
} ... the else { 
  statement body n-; 
} 
procedure: 
determination value comparison expression 1, true statement 1 is executed, if the end of the statement, to false 
if the comparison value of the expression 2 , true statement 2 is executed, the end of the if statement, false is executed statement thereof n

NOTE: The difference between the if statement and the ternary operator:

First, three can be achieved, if the statement can be achieved, not vice versa

Secondly, ternary an operator, after the implementation of which would certainly produce a result, can not produce an output statement; if statement may be implemented to generate an output statement

switch statement 
format: 
switch (expression) {
   Case Value 1: 
  Statement body 1; 
  BREAK ;  
   Case Value 2: 
  ; statement body 2 
  BREAK ;   
  ... 
  default : 
  statement n-body; 
  BREAK ;   
} 
Process: 
Case of the listed value based on the order and comparing the value of the expression, if it is true, the statement is executed the body, it encounters a break or the right brace}, the switch end of the statement. If the values are not matched to the case of, default statement is executed corresponding n body

note:

. A switch expression can accept data types:

Basic types: byte, short, char, int

Reference types: enumeration (JDK1.5 above), String string (JDK1.7 above)

b. values ​​only after case is constant, not variable, and the value of a switch case can no longer appear in the same sentence

. c Finally a break can be omitted, but is not recommended; other break must not be omitted, otherwise there will be case penetrate

d. default no matter what position it is finally implemented, it is on the final recommendation, easy to read

and if usage scenario switch: 
switch is recommended when using a fixed value determination; 
if Analyzing recommended when used interval or range

③. Loop structure

Category: for statement, while statement, do ... while statement

for statement 
format: 
for (initial expression; conditional expressions; after cyclic operation expression) { 
  loop body; 
} 
Process: 
1. perform the initial expression 
2 of a condition expression 
true, proceed to 
false, the loop ends 
3. Run loop statement 
4. after execution cycle operation expression 
5. Return to step 2 to continue to 

give chestnut: 
statistical sum of an even number within 1-100 
int sUM = 0; 
for (int I = 0; I <= 100; I + 2 =) { 
　　SUM = I +; 
} 
another implementation:

for(int i=0; i<=100; i++){
  if(i%2==0){
    sum += i;
}

while statement 
basic format: 
while (judgment condition statement) { 
  loop statement; 
} 
full format: 
initialization statement; 
while (judgment condition statement) { 
  loop statement; 
  controlling conditional statement; 
} 

Process: 
1. Perform initialization statement 
2. Analyzing execution conditional statements 
true, proceed to 
false, the loop ends 
3. execution loop statement 
4. A conditional statement execution control 
5. Return to step 2 to continue

do ... the while statement 
basic format: 
do { 
  loop statement; 
} the while (judgment condition statement); 

Full Format: 
initialization statement; 
do { 
  loop statement; 
  controlling conditional statement; 
} the while (judgment condition statement); 

flow:
 1 perform initialization statement
 2 . statement execution cycle body
 3 . performs control conditional statement
 4 . statement execution determination condition
 to true , proceed
 to false , the end of cycle
 5. Go back to step 2 to continue

Note: Three loop differences

1.do ... while loop will execute at least one loop; while for and while loops must first determine whether the conditions established, and then decide whether to execute the loop body statement

After 2.for statement is executed, the initial definition of variables will be released, it can not be used; and after the while statement is executed, initialization of variables can continue to use

Two simple endless loop manner:

 . ①the while(to true) {
  loop statement;
}

②.For(;;) {
  loop statement;
}

Nested loop:

Output * 
     ** 
     *** 
     ****   shape 

for ( int I =. 1; I <=. 4; I ++ ) {
   for ( int J =. 1; J <= I; J ++ ) { 
    Sout ( "*" ); 
} 
  Sout (); // wrap 
}

 ---------------------------- gorgeous dividing line ---------- ------------------- 

9 * 9 multiplication table 

for ( int I =. 1; I <= 9; I ++ ) {
   for ( int J =. 1; J <= I ; J ++ ) { 
    Sout (J + "*" + I + "=" + (I * J) + '\ T'); // \ T escape character, corresponding to the Tab key 
} 
  Sout ();// wrap 
} 

Summary: row number of outer-loop control, the inner loop controls the number of columns of small expansion: escape character 

 '\ T' : the Tab key
 '\ R & lt' : Enter
 '\ n-' : newline
 '\ "' : double quotes
 '\' ':apostrophe

(2) The control jump statements

Category: break, continue, return

①.break statement

Only use switch statements and loops in the role is out of the loop

②.continue statement

Can only use the loop statement , is to terminate this cycle, the next cycle continues

③.return statement

Function is returned, to the end of the process

 

Part II will begin on methods ,, BB ....

Ha ha ha ... code did not move to eat ,,