Java Variable Types

A  variable provides us with named storage that our programs can manipulate. Each variable in Java has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable. You must declare all variables before they can be used. The basic form of a variable declaration is shown here:

data type variable [ = value][, variable [= value] ...] ;

int a, b, c; // Declares three ints, a, b, and c.
int a = 10, b = 10; // Example of initialization
byte B = 22; // initializes a byte type variable B.

There are three kinds of variables in Java: 

Local variables 

Instance variables

Class/static variables

Local variables:

1. Local variables are declared in methods, constructors, or blocks. 
2. Local variables are created when the method, constructor or block is entered and the variable will be destroyed once it exits the method, constructor or block.
3. Access modifiers cannot be used for local variables. 
4. Local variables are visible only within the declared method, constructor or block.

 

Local variables are implemented at stack level internally.

 

There is no default value for local variables so local variables should be declared and an initial value should be assigned before the first use.

Example:


Here,
age is a local variable. This is defined inside pupAge() method and its scope is limited to this method only. public class Test{ public void pupAge(){ int age = 0; age = age + 7; System.out.println("Puppy age is : " + age); } public static void main(String args[]){ Test test = new Test(); test.pupAge(); } } This would produce the following result: Puppy age is: 7

Example:


Following example uses
age without initializing it, so it would give an error at the time of compilation. public class Test{ public void pupAge(){ int age; age = age + 7; System.out.println("Puppy age is : " + age); } public static void main(String args[]){ Test test = new Test(); test.pupAge(); } } This would produce the following error while compiling it: Test.java:4:variable number might not have been initialized age = age + 7; ^ 1 error

Instance variables:



Instance variables are declared in a class, but outside a method, constructor or any block.


When a space is allocated for an object in the heap, a slot for each instance variable value is created.

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
Instance variables are created when an object is created with the use of the keyword 'new' and destroyed when the object is destroyed.


Instance variables hold values that must be referenced by more than one method, constructor or block, or essential parts of an object's state that must be present throughout the class.


Instance variables can be declared in class level before or after use.


Access modifiers can be given for instance variables.


The instance variables are visible for all methods, constructors and block in the class. Normally, it is recommended to make these variables private (access level). However visibility for subclasses can be given for these variables with the use of access modifiers.


Instance variables have default values. For numbers the default value is 0, for Booleans it is false and for object references it is null. Values can be assigned during the declaration or within the constructor.


Instance variables can be accessed directly by calling the variable name inside the class. However within static methods and different class ( when instance variables are given accessibility) should be called using the fully qualified name . ObjectReference.VariableName.

Example:


import java.io.*; public class Employee{ // this instance variable is visible for any child class. public String name; // salary variable is visible in Employee class only. private double salary; // The name variable is assigned in the constructor. public Employee (String empName){ name = empName; } // The salary variable is assigned a value. public void setSalary(double empSal){ salary = empSal; } // This method prints the employee details. public void printEmp(){ System.out.println("name : " + name ); System.out.println("salary :" + salary); } public static void main(String args[]){ Employee empOne = new Employee("Ransika"); empOne.setSalary(1000); empOne.printEmp(); } }
This would produce the following result: name : Ransika

What is Singleton Class in Java? Why it is required?

The Singleton's purpose is to control object creation, limiting the number of objects to one only. Since there is only one Singleton instance, any instance fields of a Singleton will occur only once per class, just like static fields. Singletons often control access to resources such as database connections or sockets. For example, if you have a license for only one connection for your database or your JDBC driver has trouble with multithreading, the Singleton makes sure that only one connection is made or that only one thread can access the connection at a time. 
Implementing Singletons:

Example 1:
The easiest implementation consists of a private constructor and a field to hold its result, and a static accessor method with a name like getInstance(). The private field can be assigned from within a static initializer block or, more simply, using an initializer. The getInstance( ) method (which must be public) then simply returns this instance:

// File Name: Singleton.java
public class Singleton
{
 private static Singleton singleton =new Singleton();
/* A private Constructor prevents any other
 * class from instantiating. */
private Singleton()
{
}
/* Static 'instance' method */
public static Singleton getInstance()
{
 return singleton;
 }
 /* Other methods protected by singleton-ness */
protected static void demoMethod()
{
 System.out.println("demoMethod for singleton");
 }
 }

// File Name: SingletonDemo.java
public lassSingletonDemo
{
public staticvoid main(String[] args)
{
 Singleton tmp =Singleton.getInstance(); tmp.demoMethod();
}
}

This would produce the following result:
demoMethod for singleton

What are the limitations of Selenium?

Limitations are as follows:

1. It does not support non web-based applications, it only supports web based applications.
2. It is open source tool so technical issues can be resolved by selenium community forums.
3. You need to know at least one of the supported language very well in order to automate your application.
4. No inbuilt reporting capability, for this you need plugins like JUnit and TestNG for test reports.
5. Identifying the locators that support common attributes like id, names etc as well as XPATH, javascript DOM and others (Use firebug for finding the locators)
6. Selenium IDE does not supports loop and data driven testing.
7. No option to verify the images.

I will keep posting concepts related to Selenium along with QTP/UFT.