1. Method of Classes
Chapter 7, page 155
Lecture 8
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2. Review Overloading Methods Using objects as parameters
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Overloading Methods
Using objects as parameters
Argument passing
Returning objects
Recursion
Access control
Understanding static
Nested and inner classes
String class

3. Overloading Methods
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Overloading means more than two methods with the same class that share the same name.
This method is called method overloading.
This is one of the ways that Java implements polymorphism.
Class overload {
void test() {
//no argument }
void test(int a) {
//one argument
void test(int a, int b) {
// two arguments

4. Example of four methods
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5. Overloading Constructors
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Constructor is to initialize the values

6. Example of three constructors
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7. Using Objects as parameters
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We could also pass objects to methods

8. Example
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ob1 will check with
ob2 using equal(test o)

9. Argument passing
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In java, there are two ways of passing arguments, call-by-value and call-by-reference
Call-by-value will pass the value to the method or subroutine. It will not modify the original data.
Call-by-reference will pass the object to the method or subroutine. It might modify the original data depending on the method.

10. Call-by-value, there is no change in a and b in the lecture65{}, but change in test{}
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11. Call by object
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12. Returning the objects A method can return any type of data.
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A method can return any type of data.
The return type can be class types or values

13. Example of returning an object, tmp
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14. Recursion
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Recursion is the process of defining something in terms of itself.
It is a method to call itself.
For example,
1, 1, 2, 3, 5, 8, 13 etc.
Here, 2 = n(2) = n(1) + n(0)
3 = n(3) = n(2) + n(1)
5 = n(0) =1, n(1) =1

15. Example of recursion
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16. Recursion - factorial Fact(n) means n*(n -1)*(n – 2)*(n-3)…3*2*1
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Fact(n) means n*(n -1)*(n – 2)*(n-3)…3*2*1
For example, n = 3, fact(3) = 3*2*1 = 6
n = 4, fact(4) = 4*3*2*1 = 24
The relationship is
fact(1) = 1
fact(n) = n*fact(n-1)

17. Example of recursion, page 169
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n = 1, 2, 3, 4, 5
fact = 1, 2, 6, 24, 120

18. Access control
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We can specify which part of program can be accessed. This will prevent misuse.
There are three access specifiers that are used in Java. They are public, private and protected.
public: that member can be accessed by any other code
private: member can only be accessed by other members of its class

19. Example – difference between public and private
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cannot directly access
through a method

20. As a is defined as default, we can access it.
Explanation
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As a is defined as default, we can access it.
b is also defined as public, we can also access it.
c is defined as private and we cannot access it, we have to access it through a method.

21. Understand static
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Sometimes, we want to define a class member that will be used independently of any object of that class. We used the definition of static (initial value).
When a member is declared static, it can be accessed before any objects of its class are created.
main() is declared as static.
We can also declare a static block which gets executed first (before main()).

22. Example
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sequence of execution 2 4 3

23. Explanation
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While loading the program, this program will set i = 1 and j = 2,
it executes the static block to compute the value of i (4 = 3 + 1) and j (6 = 2 + 4).
It then executes main() and call String show() to display the value.

24. Example – without static
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25. Example – more
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output 1 4 2 3

26. A B Nested Classes We can define a class within another class.
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We can define a class within another class.
This class is called nested class.
The scope of a nested class is bounded by the enclosing class.
If class B is defined within class A, then B is known to A, but not outside A. A B

27. More about nested class
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There are two types of nested classes: static and non-static.
A static nested class is one which has the static modifier applied.
Because it is static, it must access the members of its enclosing class through an object.
The most important type of nested class is the inner class.

28. Example of inner class
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29. Explanation The program will execute static void main()….
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The program will execute static void main()….
It then create a new object called outer().
Outer() then defines the value outer_val and call inner class.
The inner class is to display the value of outer_val.

30. Example of generating error
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here, y is decared
outside the inner
class. Thus it is
not known here

31. String class
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String is the most commonly used class in Java’s class library.
Every string that we created is an object of type String.
System.out.println(“I am a DCO student.”);
“I am a DCO student” is a String. It can be rewritten as:
String name =“ I am a DCO student.”
System.out.println(name);

32. Example
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33. Summary Overloading Methods – two or more methods with the same class
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Overloading Methods – two or more methods with the same class
Using objects as parameters – pass object
Argument passing – value and object
Returning objects – return any data type
Recursion – calling itself
Access control – public, private and protected
Understanding static- initial value
Nested and inner classes – a class within a class
String class – each string is an object