1. CS139
October 11, 2004

2. Review of TestNamesV1 Within the class, call method using its name.
If a procedure (void return type), simply call the procedure as a statement. Pass in appropriate values in the argument list.
Ex:
displayName( name1 ) ;
If a function (returns a value), call or invoke the function by using an assignment statement or by invoking the function where you want to use the value.
System.out.println( name1.firstMiddleLast() ) ;
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3. Method Overloading (Chapter 6 )
Method overloading is the process of giving a single method name multiple definitions
If a method is overloaded, the method name is not sufficient to determine which method is being called
The signature of each overloaded method must be unique
The signature includes the number, type, and order of the parameters
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4. Method Overloading
The compiler determines which method is being invoked by analyzing the parameters
float tryMe(int x) {
int out;
out = x ;
return out; }
result = tryMe(25, 4.32)
Invocation
float tryMe(int x, double y) {
int out;
out = x * y;
return out; }
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5. Method Overloading The println method is overloaded (see page 860):
println (String s)
println (int i)
println (double d)
and so on...
The following lines invoke different versions of the println method:
System.out.println ("The total is:");
System.out.println (total);
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6. Overloading Methods
The return type of the method is not part of the signature
That is, overloaded methods cannot differ only by their return type
Constructors can be overloaded
Overloaded constructors provide multiple ways to initialize a new object (See next slide)
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7. Constructor Overloading – An Example
public class Name { private String fName , mName, lName ; // Name parts public Name( String first, String middle, String last) { fName = first ; mName = middle ; lName = last ; }
public Name( String first, String last) {
fName = first ; mName = “” ; lName = last ; } }
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8. Constructors
A class with no constructor methods uses a “default” constructor.
Default constructor builds the data areas, but does not explicitly initialize instance variables.
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9. Conditionals and Loops (Ch. 5)
Now we will examine programming statements that allow us to:
make decisions
repeat processing steps in a loop
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10. Flow of Control
Unless specified otherwise, the order of statement execution through a method is linear: one statement after another in sequence
Some programming statements allow us to:
decide whether or not to execute a particular statement
execute a statement over and over, repetitively
These decisions are based on boolean expressions (or conditions) that evaluate to true or false
The order of statement execution is called the flow of control
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11. Conditional Statements - 1
A conditional statement lets us choose which statement will be executed next
Therefore they are sometimes called selection statements
Conditional statements give us the power to make basic decisions
The Java conditional statements are the:
if statement
if-else statement
switch statement
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12. Conditional Statements - 2
Let us simulate decisions in the “real world”.
If it is raining, then I will take my umbrella to work, otherwise, I will leave it at home.
The “take my umbrella” action is conditioned on the result of the decision, if it is raining, which asks the question “is it raining?”.
When building selections, always think about both pieces – what do I do if this decision is true, what do I do if this decision is false.
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13. The if Statement The if statement has the following syntax:
The condition must be a
boolean expression. It must
evaluate to either true or false.
if is a Java
reserved word
if ( condition )
statement;
If the condition is true, the statement is executed.
If it is false, the statement is skipped.
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14. Logic of an if statement
condition
evaluated
false
statement
true
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15. Boolean expression
An arithmetic expression’s evaluation results in some numeric result.
A Boolean expression’s evaluation results in either a true or a false result. See Schaum’s for lots of Boolean expression examples.
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16. Boolean Expressions
A condition often uses one of Java's equality operators or relational operators, which all return boolean results:
== equal to
!= not equal to
< less than
> greater than
<= less than or equal to
>= greater than or equal to
Note the difference between the equality operator (==) and the assignment operator (=)
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17. The if Statement - 1 An example of an if statement:
delta = 0 ;
if (sum > MAX)
delta = sum - MAX;
System.out.println ("The sum is " + sum);
First the condition is evaluated -- the value of sum is either greater than the value of MAX, or it is not
If the condition is true, the assignment statement is executed -- if it isn’t, it is skipped.
Either way, the call to println is executed next
See Age.java (page 208)
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18. The if Statement - 2
An if statement may conditionally execute a block of statements, not just one statement.
if (sum > MAX) {
delta = sum - MAX;
sum = MAX ; }
System.out.println ("The sum is " + sum);
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19. Indentation
The statement controlled by the if statement is indented to indicate that relationship
The use of a consistent indentation style makes a program easier to read and understand
Although it makes no difference to the compiler, proper indentation is crucial
"Always code as if the person who ends up maintaining your code will be a violent psychopath who knows where you live."
-- Martin Golding
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20. The if-else Statement
An else clause can be added to an if statement to make an if-else statement
if ( condition )
statement1;
else
statement2;
If the condition is true, statement1 is executed; if the condition is false, statement2 is executed
One or the other will be executed, but not both
See Wages.java (page 211)
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21. Lab Tomorrow
We will practice some if/else statements using prior labs. Make sure you have the Circle class and the Names class available for lab.
There will also be a practice exercise available to let you practice evaluating boolean expressions.
This should be done Tuesday night and is due in class on Wednesday.
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