Methods

1
Methods

• Homework Solutions
• 7
• 2) 1
• 3) 9
• 4) Runtime Error infinite loop
• (actually, int overflow reported answer is
  1339571480)
• 5) 5

• 6) Compiler Error
• cannot find symbol
• variable count.
• 7) 0
• 8) X final value 4
• Y final value 7
• Sum 13
• Product 90

2
Method basics

• Always
• represents a series of commands.
• ends with parentheses
• begins with lowercase letters
• Sometimes
• returns a value
• requires information

3
Examples

• String str What is up?
• str str.toUpperCase()
• Person p new Person()
• p.setPetsName(Apollo)
• int dudesAge p.getAge()

returns a value becomes a new String object
No extra info required.
Extra info required in order for method to
execute.
returns a value becomes a new int primitive
Does not return a value doesnt turn into
anything just a command
4
Complex method calls

• person1.setName(person2.getName())
• String str The Detroit Tigers
• are the best team in
• all of baseball.
• String sport str.substring(
• str.indexOf(base),
• str.indexOf(.))

returns a String object.
returns an int
returns an int
5
Two kinds of methods

• Ordinary methods
• operate on a particular object
• p.setName(Freddy)
• str.charAt(3)
• acc.deposit(123.45)
• b1.addActionListener(this)
• rect.getArea()
• static methods
• operate from a class
• context is separate from individual objects.
• Math.sqrt(9.0)
• Account.updateAllAccounts()
• Person.numObjectsCreated()
• Fish.pondTemperature()
• Time.valueOf(123400)

6
The Math Class

• The Math class API
• All methods are static.
• Basic methods
• abs(double a)
• abs(int a)
• max(double a, double b)
• max(int a, int b)
• min(double a, double b)
• min(int a, int b)
• pow(double a, double b)
• random()
• squrt(double a)

7
Overloaded Methods

• When a class uses the same method name more than
  once, the method is said to be overloaded.
• Math.abs(2) //no confusion!
• Math.abs(2.1) //no confusion!
• Java knows which method to use from the parameter
  type.
• Must use a new permutation of parameter types to
  reuse a method name.

8
Practice

• Pretend you have a Person class with the
  following methods
• getName() setName(String n)
• getAge() setAge(int a)
• Write a line of code that creates a Person
  object.
• Write a line of code that gives this person a
  name.
• Write a line of code that gives this person an
  age.
• Write a line of code that creates a String object
  called xName and assigns to it the name of your
  person. (Pretend you have forgotten the name.)
• Write a line of code that creates an int
  primitive variable called xAge and assigns to it
  the age of your person. (Again, pretend you have
  forgotten the age.)