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Variables in Java
What is a Variable?
Variable plays an important role when you are coding in java. We use Java variables to store information to be referenced and manipulated in our java programs. Variables can store data value in our programs like a container.
Variable is the name of a memory location. We use variable names in our program instead of using use memory locations directly in our code.
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Identifiers in Java is used to identify the class, constant, array, method names. List down rules to declare identifiers and explore java reserved keywords
ONE MISTAKE in VIDEO : The term Access specifier is used by c++ programmers not in java. In JAVA Officially we use ACCESS MODIFIER but i have used access spe...
What is variable ?
1. Variable is a name of memory location where data is stored. 2. The value of variable can vary, means value can be changed. There are three types of variables : 1. Local Variables : 1.1 DECLARED : inside methods, constructors or blocks. 1.2 SCOPE : within the methods, constructors or blocks but not outside of them. 1.3 MEMORY ALLOCATION : when method, constructor or block is invoked variable is allocated; when exits, variable gets destroyed. 1.4 STORED MEMORY : stack memory 1.5 DEFAULT VALUES : doesnt have any default value, so it should be assigned before use. 1.6 ACCESS MODIFIERS : public, private or protected access specifier cannot be used. 2. Instance Variable : 2.1 DECLARED : in a class but outside methods, constructors or blocks. 2.2 SCOPE : inside the class, within all methods, constructors or blocks. 2.3 MEMORY ALLOCATION : when object is created, variable allocated memory; when object destroyed, memory releases. 2.4 STORED MEMORY : heap memory 2.5 DEFAULT VALUES : have default values eg. int has 0 value, boolean false, String null etc. 2.6 ACCESS MODIFIERS : any access modifiers can be used. 2.7 HOW TO ACCESS : a) can be accessed directly by calling the variable name inside the class. b) in static methods they should be called using the fully qualified name, ie objectRefName.variable_name. 3. static variable : 3.1 DECLARED : with static keyword in a class but outside methods, constructors or blocks. 3.2 SCOPE : similar to instance variable ie inside the class, within all methods, constructors or blocks including static part 3.3 MEMORY ALLOCATION : when we run program and .class file is loaded, variable allocated; when class file unload, variable gets destroyed. 3.4 STORED MEMORY : non-heap memory or static memory 3.5 DEFAULT VALUES : have default values eg. int has 0 value, boolean false, String null etc. 3.6 ACCESS MODIFIERS : any access modifiers can be used. 3.7 HOW TO ACCESS : a) directly b) by using class name b) by using object reference name
ONE MISTAKE in VIDEO : The term Access specifier is used by c++ programmers not in java. In JAVA Officially we use ACCESS MODIFIER but i have used access spe...
What is variable ? 1. Variable is a name of memory location where data is stored. 2. The value of variable can vary, means value can be changed.
There are three types of variables : 1. Local Variables : 1.1 DECLARED : inside methods, constructors or blocks. 1.2 SCOPE : within the methods, constructors or blocks but not outside of them. 1.3 MEMORY ALLOCATION : when method, constructor or block is invoked variable is allocated; when exits, variable gets destroyed. 1.4 STORED MEMORY : stack memory 1.5 DEFAULT VALUES : doesnt have any default value, so it should be assigned before use. 1.6 ACCESS MODIFIERS : public, private or protected access specifier cannot be used.
2. Instance Variable : 2.1 DECLARED : in a class but outside methods, constructors or blocks. 2.2 SCOPE : inside the class, within all methods, constructors or blocks. 2.3 MEMORY ALLOCATION : when object is created, variable allocated memory; when object destroyed, memory releases. 2.4 STORED MEMORY : heap memory 2.5 DEFAULT VALUES : have default values eg. int has 0 value, boolean false, String null etc. 2.6 ACCESS MODIFIERS : any access modifiers can be used. 2.7 HOW TO ACCESS : a) can be accessed directly by calling the variable name inside the class. b) in static methods they should be called using the fully qualified name, ie objectRefName.variable_name.
3. static variable : 3.1 DECLARED : with static keyword in a class but outside methods, constructors or blocks. 3.2 SCOPE : similar to instance variable ie inside the class, within all methods, constructors or blocks including static part 3.3 MEMORY ALLOCATION : when we run program and .class file is loaded, variable allocated; when class file unload, variable gets destroyed. 3.4 STORED MEMORY : non-heap memory or static memory 3.5 DEFAULT VALUES : have default values eg. int has 0 value, boolean false, String null etc. 3.6 ACCESS MODIFIERS : any access modifiers can be used. 3.7 HOW TO ACCESS : a) directly b) by using class name b) by using object reference name
Variables in Java are classified into two categories 1. primitive type and reference type . variables are of two types local variables and instance variables
