Lecture java continued
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The lecture introduces object-oriented programming (OOP) concepts, particularly focusing on access control modifiers such as private, package, protected, and public. It explains the relationship between classes and objects, including how objects are instances of classes and can access class members. Additionally, it covers the purpose of constructors in Java for initializing objects and demonstrates how constructors can take parameters.
![public class Pencil {
public String color = “red”;
public int length;
public float diameter;
private float price;
public static long nextID = 0;
public void setPrice (float newPrice) {
price = newPrice;
}
}
public class CreatePencil {
public static void main (String args[]){
Pencil p1 = new Pencil();
p1.price = 0.5f;
}
}
Pencil.java
CreatePencil.java
%> javac Pencil.java
%> javac CreatePencil.java
CreatePencil.java:4: price has private
access in Pencil](https://image.slidesharecdn.com/lecturejavacontinued-220221185918/85/Lecture-java-continued-3-320.jpg)
Lecture java continued
- 1. Object-Oriented Programming Dr. Riaz UlAmin Lecture : Introduction to OOP
- 2. More about field modifiers (1) Access control modifiers – private: private members are accessible only in the class itself – package: package members are accessible in classes in the same package and the class itself – protected: protected members are accessible in classes in the same package, in subclasses of the class, and in the class itself – public: public members are accessible anywhere the class is accessible
- 3. public class Pencil { public String color = “red”; public int length; public float diameter; private float price; public static long nextID = 0; public void setPrice (float newPrice) { price = newPrice; } } public class CreatePencil { public static void main (String args[]){ Pencil p1 = new Pencil(); p1.price = 0.5f; } } Pencil.java CreatePencil.java %> javac Pencil.java %> javac CreatePencil.java CreatePencil.java:4: price has private access in Pencil
- 6. An object is an instance of a class. A class is a template or blueprint from which objects are created. So, an object is the instance(result) of a class.
- 10. Access Members of a Class We can use the name of objects along with the . operator to access members of a class. For example,
- 12. In the above example, we have created a class named Bicycle. It includes a field named gear and a method named braking(). Notice the statement, Bicycle sportsBicycle = new Bicycle(); Here, we have created an object of Bicycle named sportsBicycle. We then use the object to access the field and method of the class. sportsBicycle.gear - access the field gear sportsBicycle.braking() - access the method braking()
- 15. Constructors A constructor in Java is a special method that is used to initialize objects. The constructor is called when an object of a class is created.
- 17. Constructor Parameters Constructors can also take parameters, which is used to initialize attributes. The following example adds an int y parameter to the constructor. Inside the constructor we set x to y (x=y). When we call the constructor, we pass a parameter to the constructor (5), which will set the value of x to 5: