Classification of control statements in Java:
(1) Branch statement: if-else, switch.
(2) Loop statement: while, do-while, for.
(3) Jump statements: break, continue, return.
(4) Exception handling statement: try-catch-finally, throw.
(5) Package processing statement: package, import.
(6) Comment statement: //, / *… /, / ** … /
Standard if-else statement
The third format of if statement: if…else if…else
if (judgment condition 1) { execution statement 1; }else if (judgment condition 2) { execution statement 2; } … }else if (judgment statement n) { execution statement n; }else{ execute statement n+1; }
Implementation process
First judge the relational expression 1 to see whether the result is true or false.
If it is true, execute the statement body 1 and
if it is false, execute the statement body 2.
if… else if …else
switch statement
switch (expression) { case constant value 1; statement body 1; break; case constant value 2; statement body 2; break; … default: statement body n+1; break; } first calculate the value of the expression , then, and case Comparing in turn, once there is a corresponding value, the corresponding statement will be executed. During the execution, it will end when it encounters a break. Finally, if all the cases do not match the value of the expression. The body of the default statement will be executed, and the program will end. 1. The values behind multiple cases cannot be repeated . The parentheses after switch can only contain the following data types; basic data types: byte/short reference data types: String string, enum enumeration
for loop statement format
for (initialization expression 1; Boolean expression 2; stepping expression 4) {
loop body 3
}
execution flow
Execution sequence: 1234>234>234...2 until it is not satisfied.
1 Responsible for completing the initialization of loop variables
2 Responsible for judging whether the loop condition is full, and jumping out of the loop if it is not satisfied
3 County executes the statement
4 After the loop, the change of variables involved in the loop condition
Standard format of do-while/for-while loop statement
do{
loop body
} whiIe (conditional judgment);
extended format:
initialization statement
do{
loop body
step statement
}While (conditional judgment);
Loop control statement continue keyword
Once executed. Immediately skip the remaining content of the current cycle, and immediately start the next cycle
Ternary operator and standard if-else statement
for-if statement
Exercise after class: use loops to calculate even numbers between 1-100
