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Concept Normally, statements in Java are executed sequentially in the order written in the source code. Control statements are used to modify the order of execution of statements. Most control statements are conditional ; that is, the next statement to be executed depends on the result of evaluatingan expression, usually, an expression that returns a boolean value of true or false.
These source code of these learning objects can be found in control.zip .
| LO | Topic | Java Files (.java) | Prerequisites |
| "If-statements" | If-statements | Control01 | |
| "Conditional expressions" | Conditional expressions | Control02 | 1 |
| "While loops" | While loops | Control03 | |
| "Do-while loops" | Do-while loops | Control04 | |
| "Break statements" | Break statements | Control05 | 3 |
| "Counting with for statements" | Counting with for statements | Control06 | |
| "General for statements" | General for statements | Control07 | 6 |
| "Continue statements" | Continue statements | Control08 | 6 |
| "Switch statements" | Switch statements | Control09 |
Concept The execution of an if-statement starts with the evaluation of
its boolean-valued expression. If the result is true, the statement writtenafter the closing parenthesis of the expression is executed; if the result is
false, the statement written after the
else is executed. These statements
can be single statements or blocks of statements. In particular,the statements can themselves be if-statements (
nested if-statements ),
in which case the inner statement is executed the same way.
Program: Control01.java
// Learning Object Control01
// if statementspublic class Control01 {
public static void main(/*String[] args*/) {
int year = 2000; int month = 6;
int days; if (month == 2)
if (year % 4 == 0) days = 28;
else days = 29;
else if (month == 4 || month == 6 || month == 9 || month == 11)
days = 30; else
days = 31; System.out.println(days);
}}
The program computes the number of days in a month taking leap years into account.
year and
month , are
given initial values.month == 2 evaluates to false, so the statement
following the else is executed. Jeliot will display
Choosing else-branch to
emphasize this.|| (or) becomes
true, there is no need to evaluate the others.Choosing then-branch . (The
terminology
then-branch orginates from programming
languages that require the use of the keyword
then between the expression
and the statement.)days is printed.Exercise Complete the program with the correct computation for leap years: a year divisible by 100 is not a leap year unless itis also divisible by 400.
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