DataStructures-And-Algorithms.

Data Structures :-

Data Structures is a way of storing/organising data in the memory, in such a way that access, management and modification become efficient.

Algorithms :-

Algorithms is any approach you use to perform operations on data (like searching, sorting, traversing, ..Etc.).

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Prerequisites :-

0. PROGRAMMING LANGUAGE.
1. CLASS AND OBJECTS.
2. CONSTRUCTOR.
3. this KEYWORD.
4. ACCESS MODIFIERS IN JAVA.

• Public- The access level of public modifier is everywhere. Methods, variables declared public can be accesed from anywhere after importing that class.

• Default- The access level of default modifier is within package. Methods, variables declared default can be accesed from other classes of same package.

• Private- The access level of private modifier is within the class. Methods, variables declared private cannot be accesed from outside the class.

5. ENCAPSULATION.
6. STATIC KEYWORD IN JAVA.
7. • You can call static methods from non static method but reverse is not true.
8. INNER CLASS IN JAVA.
9. Pass by value.
10. Pass by refrence.

import java.util.*;

public class Hi {

	// here value is copied in localVariable 'a'.
	public static void incrementPrimitiveDT(int a) {
		a++;
	}

	// here reference is copied, means 'input' is also pointing to 'arr'.
	public static void incrementReferenceDT(int input[]) {
		for(int i=0;i<input.length;i++) {
			input[i]++;
		}
	}


	public static void main(String[] args) {
		int i=10;
		incrementPrimitiveDT(i); // passByValue
		System.out.println(i); // 10


		int arr[]= {1,2,3,4,5};
		incrementReferenceDT(arr); // passByReference
		System.out.println(Arrays.toString(arr)); // [2, 3, 4, 5, 6]
	}
}

10. Strings are immutable.
11. == & .equals in String.
12. Wrapper class in java.

    • Object creation and memory allocation in Integer class.

    public static void main(String[] args) {
		// case 1:
				Integer i= new Integer(1);
				Integer j=new Integer(1);
				System.out.println(i==j); // false,  coz == check reference address of i and j, and here 'i' is pointing to 1 (i---> 1) and 'j' is pointing to different 1 (j---> 1)
				System.out.println(i.equals(j)); // true

		// case 2:
				Integer a=new Integer(2);
				Integer b=2;

				System.out.println(a==b); // false
				System.out.println(a.equals(b)); // true

		// case 3:
				Integer x=new Integer(3);
				Integer y=x;

				System.out.println(x==y); // true
				System.out.println(x.equals(y)); // true


		// case 4
				Integer p=128;
				Integer q=128;
				System.out.println(p==q); // false
				System.out.println(p.equals(q)); // true

		// case 5 -128 to 127 is in cached memory so they point to same object without creating it instances.
				Integer s=50;
				Integer t=50;
				System.out.println(s==t); // true
				System.out.println(s.equals(t)); // true
    }

13. Generics in Java.

14. isequals and hashcode in java by codingSimplified.

    • isequals and hashcode in java by AnujBhaiya.

15. % operator in JAVA : dividend % divisor - Here two statement is needed to be taken care :-

    • When Divedend < Divisor then answer is dividend.

    • When Divedend > Divisor then answer lie in between [0 to divisor-1].

16. Store 2 numbers in a number.

    • To Inject B in A we ADD(+) B*INF in A and store it in A, where INF is any number greater than A and B.
    • to extract old number i.e., A from modified A we do (A % INF).
    • to extract new number(Injected number) i.e., B from modified A we do (A / INF).

    	int a=5;
    	int b=4;// number to be injected
    	int INF=9999;
    	a=a+(b*INF);
    	System.out.println(a%INF); // 5
    	System.out.println(a/INF); //4

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1. Memory Allocation when you initialize a variable.

• Note : When there is no reference variable pointing to actual object then it is deleted automatically when garbage collection hits.

2. Objects & Reference Variable.

public class Demo{ 
	public static void main(String[] args) {
			Human obj=new Human();
			Human son=obj; // this is his mom who call obj as hisSon.
			Human bro=obj; // this is his sis who call obj as hisBro.
			son.hairCut="done"; // here his mom made him do haircut.
			// here his sister is also able to see his haircut.
			System.out.println(bro.hairCut); // done
		
	}
}
class Human{
	String name="Vikash";
	String hairCut="notDone";
}