OOP using java (Variable in java)
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The document provides an overview of variables in Java, including their definition, memory allocation, and types such as instance, local, and class (static) variables. It explains how to declare variables and emphasizes the role of constructors in object creation. Key points include the importance of reinitializing variables within methods and the shared nature of static variables among class instances.
OOP using java (Variable in java)
- 1. OOP - JAVA Variables in Java 4/6/2022 1 Department of Computer PRO – GRADE 5 Lecturer. OMEED M. M
- 2. Table of contents What is Variable? Allocating memory Types of variables Constructor 4/6/2022 2
- 3. Variable in Java Variables used to store in our computer’s memory Why called it variable? Because the values inside the variables are changeable. Attributes - things that the object stores data in, generally variables. Methods - Functions and Procedures attached to an Object and allowing the object to perform actions 4/6/2022 3
- 4. Allocating memory In order to store some data in our computer memory we have to allocate some space so how we can do that? we will go through allocating memory, 4/6/2022 4
- 5. Allocating memory For this purpose we have to declare variables. How we can declare variable we are going to using assignment We can assign a value to a variable by using (Equal =) operator. Ex. String ANY_NAME = “ANY_NAME” 4/6/2022 5
- 6. Variable in Java • Re-difine variable 4/6/2022 6
- 7. Variable in Java • Println 4/6/2022 7
- 8. Types of variables There are Three type of variables:- 1. Instance variables 2. Local variables 3. Class variables (Static variables) 4/6/2022 8
- 9. Instance variables Instance variables Declared inside class but not inside method. Ex. Class test{ Int data=15; //instance variable Float pi=3.114f; //instance variable } Cannot be reinitialized directly within class Ex. Class test{ Int data=15; //instance variable data =20; //Error for correction we have to put it into a method void testMethod(){ data=20 // correct; } } 4/6/2022 9
- 10. Local variables Local variables – Declared inside method or method parameters. Ex. Int areatest (int radius){ Int total = radius * radius; Return total; } -These are not accessible outside method. -They did not get default values. 4/6/2022 10
- 11. Class / Static variables Class variables − are variables declared within a class, outside any method, with the static keyword -Static variable is shared between all objects because it belong to the class. It does not belong to the object -A static variable can be accessed without creating an instance of the class. 4/6/2022 11
- 12. Constructor A constructor in Java is similar to a method that is invoked when an object of the class is created. Unlike Java methods, a constructor has the same name as that of the class and does not have any return type. For example, class Test { Test() { // constructor body } } 4/6/2022 12
- 13. Types of variables class A{ int date=50; //_________ variable static int m=100; //_________ variable void method(){ int n=90; //________ variable } } //end of class 4/6/2022 13
- 14. Any Questions ? 4/6/2022 14