QA's approach 2 Java - Problems & Solutions to Information storage in Java
4 ways to store information in java:
1. Using Variables
Variable is a container to hold only one value.
When to use?
When we want to store only one value.
Limitations: Can store only one value
if we require to store 120 values, we need 120 variables which will be placed at dis- continuous memory locations, so we have below 2 problems.
Problem 1:
Reading problem:
Data is stored at some random location, hence requires more time for reading it.Limitations: Can store only one value
if we require to store 120 values, we need 120 variables which will be placed at dis- continuous memory locations, so we have below 2 problems.
Problem 1:
Reading problem:
Problem2:
Sending problem:
If we take individual primitive variable, we cannot pass multiple values beyond the parameter we defined.
If we take individual primitive variable, we cannot pass multiple values beyond the parameter we defined.
2. Using Class objects
When to use?
When we store multiple, fixed no of values of different types
Arrays: Stores homogeneous elements of fixed size
Example:
Int[] a = new int[10]; //Primitive type array
Integer a[]=new Integer[20]; //Wrapper type array
Example Ex1=new Example[5]; //User defined Class type array
Object array: Stores dissimilar or heterogeneous elements of fixed size
Object obj[]=new object[20];
can store combination of primitive, reference, user defined elements
Primitive array object can store its own primitive type or its sub types which are of lower range only will be accepted
Employee class object cannot be stored in Student array object.
Student class array can only store student class objects or its sub class objects(i.e., its child class objects)
Class array:
When it comes to classes, its own class objects or its sub class objects can be stored
Class array object contains referenced variables in continuous memory locations.
3. Using array objects
When to use?
When we want to store multiple, fixed no of values of same type, in continuous memory locations
Arrays: Stores homogeneous elements of fixed size
Example:
Int[] a = new int[10]; //Primitive type array
Integer a[]=new Integer[20]; //Wrapper type array
Example Ex1=new Example[5]; //User defined Class type array
Object array: Stores dissimilar or heterogeneous elements of fixed size
Object obj[]=new object[20];
can store combination of primitive, reference, user defined elements
There are 4 Limitations:
1.Type problem
1.1. w.r.t primitive types
1.1. w.r.t primitive types
Primitive array object can store its own primitive type or its sub types which are of lower range only will be accepted
1.2. w.r.t Class types
Employee class object cannot be stored in Student array object.
Student class array can only store student class objects or its sub class objects(i.e., its child class objects)
Class array:
When it comes to classes, its own class objects or its sub class objects can be stored
Class array object contains referenced variables in continuous memory locations.
Solution to Type problem:
Java provides inbuilt solution to type problem using inheritance
Object array is the parent class for all, creating an object class array- any type either primitive or referenced type objects can be stored as they are all sub classes to Object class.
Java provides inbuilt solution to type problem using inheritance
Object array is the parent class for all, creating an object class array- any type either primitive or referenced type objects can be stored as they are all sub classes to Object class.
2.Size
Array index out of bound
Array index out of bound
3.Storing order problem
Array by default stores the objects in insertion order & retrieves the objects in random order.
Wanted to store objects in Asc/Desc order.
Want to retrieve the objects in FIFO/LIFO.
Want to retrieve in Sequential manner.
Array by default stores the objects in insertion order & retrieves the objects in random order.
Wanted to store objects in Asc/Desc order.
Want to retrieve the objects in FIFO/LIFO.
Want to retrieve in Sequential manner.
4.Operators problem
Inbuilt supported methods are not available
Inbuilt supported methods are not available
Solution:
To solve Size, Sorting, Operators problem- collections came into picture.
To solve Size, Sorting, Operators problem- collections came into picture.
4. Using collection objects
When to use?
When we don't know the type & size of values to be sent by the end user
&
we want to store all the values as a single object
Where to use?
&
we want to store all the values as a single object
Where to use?
When user wanted to sent all the values from one application to another using a single method parameter.
Common operations performed in collection:
1. Create collection object
2. Add objects to collection
3. Return collection object or pass it as a method argument of some other program
4. Retrieve or remove or replace objects in the collection.
Common operations performed in collection:
1. Create collection object
2. Add objects to collection
3. Return collection object or pass it as a method argument of some other program
4. Retrieve or remove or replace objects in the collection.
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