There are some difference between String, String Buffer and String Builder. We discuss String and its methods. We have some more methods in String buffer and Builder to modify strings.
String is immutable, if you try to alter their values, another object gets created, whereas StringBuffer and StringBuilder are mutable so they can change their values.
String, String Buffer and String Builder
String and String Buffer
String Buffer and String builder is almost the same (excepts 2-3 differences).
You can refer this site -- gives the proper difference between these terms.
Today we are going to start a new topic and this topic is very important for interview purpose as well as for job/doing coding.
" String is a CLASS in Java.." String is a sequence of characters.
There are two ways to get string object in java
using new keyword
using literal constant
1 ) Using a new keyword.
whenever we want to create an object, we must know about the constructor of it.
String class has 2 Constructors.
no argument constructor [ String() ]
one argument constructor [ String(String s) ]
Note - Both are same no difference, just a way of writing (Syntax) is different because of the constructor.
2) literal Way
Question -- what is the diffrence between String s = new String("Hello"); and String s = "Hello"; ?
Answer -
String s1="hello";
The string literal "hello" will be created and this would be placed in the String constant pool. (constant pool is a special memory for String literal. )
Hence one object is created with s1 as a reference variable to it.
Also, when any other reference variable is created in future with the same value as "hello", it would refer to the already created String literal present in the constant pool rather than creating a new one.
String s1=new String("hello");
In this case, two objects would be created.One would be the same string literal as above and would be placed in String constant pool. The second object would be created and placed in the normal(non pool) memory and s1 would refer to it. The second object would act as a normal object in a heap.
In short,
String S1 = new String("Hello"); This statement creates a String object in the Heap Memory.
String S1 = "Hello"; This statement creates a String literal with value "Hello" in the String Pool.
For more understanding, let's take 3 cases.
Case 1. String Object and Literal
String s1 = "Hello"; String s2 = new String("Hello");
Since s1 and s2 are reference variables, they'd be pointing at their respective memory locations right ?
s1 points to String Pool's location and s2 points to Heap Memory location.
Now testing if they're equal: if(s1 == s2) would return false,as the reference variables are checked.
Whereas s2.equals(s1) will return true as equals function checks the individual characters in both the reference variables.
An Interesting Fact: "String Literal Pool" is a memory area that contains all the string literals used in the program. Whenever a new literal is encountered, the JRE checks if it exists in the String pool or not. It does not contain duplicate literals.
If you create two reference variables with the same value "Hello", they'd both point to the same location.
Case 2: Two String Literals:
Eg: String s1 = "Hello"; String s2 ="Hello";
if(s1==s2) will be true.
Case 3: One string object and anonymous literal
String s1 = new String("Hello");
if(s1 == "Hello") will be false.
In this case, "Hello" creates a literal in the pool which has a different memory location than S1's heap memory.
Here are the links and videos... You can find good programs here and please understand all logical concept from here and practice all logical programs...to become a good java developer.
Here are some logical programming question that may ask in viva or an interview. Don't by heart (mug up) these programs to try to do it by your self.
If you find any difficulty to solve these programs please comment on this post I will mail you the solutions.
# Some Logical Programs
Ques 1 - WAP of Fibonacci sequence, ask a number from user and print n terms of that Fibonacci Series.
Ques 2 - WAP to generate TABLE in proper formate
if the number is negative --- o/p will be a negative number
if the number is positive --- o/p will be table generate
if the number is string --- o/p will be enter number only.
Ques 3 - WAP to generate Factorial
With recursion
Without recursion
Ques 4 - WAP to print your name 100 times without using a loop. [Hint - using recusion]
Ques 5 - WAP to find the factorial of a given number n.
With recursion
Without recursion
Ques 6 - WAP to find the prime number from 2 to n (n is input from the user).
whatever we learn in the previous post is all about basics of an array and all pics are belongs to "Single Dimensional Array".
Now, We are going to discuss on syntax and program on it.
It is a two-step Process...
Step 1 )
These are three (3) ways to Declare An Array...
Step 2 )
Way to instantiation/initialization of an array....
This step is a combination of Step 1 and Step 2
This is a basic program to declare, initialize and display character array.
# Multi-Dimensional Array
Multi-Dimensional Array is a " MATRIX ". It has a ROW and COLUMN . But In java , we have somthing called "JAGGED ARRAY".
A jagged array in Java is a multi-dimensional array comprising arrays of varying sizes as its elements. It’s also referred to as “an array of arrays” or “jagged array”.
But you don't need to bother about terms because it works same as 2D Array (Multi-Dimensional Array) but internally it different with 2D Array.
If you want to understand it in more deep and better ways --- go to this site -- " www.baeldung.com " Detailed Description.
