CS111: PROGRAMMING LANGUAGE II Computer Science Department Lecture 1(c): Java Basics (II)
Lecture Contents Java basics (part II) Conditions Loops Methods
Conditions & Branching
Conditional Statements A conditional statement lets us choose which statement will be executed next Conditional statements give us the power to make basic decisions Java's conditional statements: the if and if-else statements the conditional operator the switch statement
The if Statement The if statement has the following syntax: if is a Java reserved word The condition must be a boolean expression. e.g., a boolean variable, a == b, a <= b. It must evaluate to either true or false. if ( condition ) statement1; else statement2; If the condition is false, this statement is executed. If the condition is true, this statement is executed.
condition evaluated true false Statement 1 Statement 2 Logic of an if-else statement Several statements can be grouped together into a block statement A block is delimited by braces ( { } )
Relational operators
Logical Operators
Loops & Iterations
Loop Statements while statement while ( condition ) statement; do statement do { statement list; } while ( condition ); for statement for ( initialization ; condition ; increment ) statement;
While loops while ( condition ) statement;
Example Look at the code and describe the output!! System.out.print( Enter a month (1 to 12): ); int month = scan.nextint(); while (month < 1 month > 12) { } System.out.println( month + is not a valid month. ); System.out.print( Enter a month (1 to 12): ); month = scan.nextint(); // set initial value of month so that the while condition // below is false initially int month = -1; while (month < 1 month > 12) { } System.out.print( Enter a month (1 to 12): ); month = scan.nextint();
do loops do { statement; } while ( condition );
Example What is the difference here?? int month; // no need to initialize month do { System.out.print( Enter a month(1 to 12): ); month = scan.nextint(); } while (month < 1 month > 12); // beginning of the next statement
for loops for ( initialization ; condition ; increment ) statement;
Example int sum = 0; for (int counter = 1; counter <= max; counter++) sum += counter; // beginning of the next statement Establish initial value of control variable. int counter = 1 Determine if final value of control variable has been reached. counter <= max false true sum+= counter Body of loop (this may be multiple statements) counter++ Incremen the control variable.
Methods A method: groups a sequence of statement takes input, performs actions, and produces output In Java, each method is defined within specific class
Method Declaration: Header A method declaration begins with a method header public class MyClass { static int min ( int num1, int num2 ) properties return type method name parameter list The parameter list specifies the type and name of each parameter The name of a parameter in the method declaration is called a formal argument
Method Declaration: Body The header is followed by the method body: class MyClass { static int min(int num1, int num2) { int minvalue = num1 < num2? num1 : num2; return minvalue; } }
The return Statement The return type of a method indicates the type of value that the method sends back to the calling location A method that does not return a value has a void return type The return statement specifies the value that will be returned Its expression must conform to the return type
Calling a Method Each time a method is called, the values of the actual arguments in the invocation are assigned to the formal arguments int num = min(2, 3); static int min (int num1, int num2) { } int minvalue = (num1 < num2? num1 : num2); return minvalue;
Method Call Stack A method can call another method, who can call another method, main min(num1, num2, num3) println() min(1, 2, 3); println( )
That s all for today.. Text Book: Chap 4 Chap 5