Find pairs of elements in Array whose sum
Four Principles of OOP
·
Inheritance
2.) Polymorphism
3.) Encapsulation
4.) Abstraction
Inheritance
·
The concept that when
a class of objects is defined, any subclass that is defined can inherit the
properties and functionalities of the class
Inheritance can be defined as the process where one class acquires the
properties (methods and fields) of another.
Polymorphism
·
The concept of
presenting an interface for differing data types
Declare a uniform interface that isn't type aware
Ability of an object to take on many forms
Encapsulation
·
There's a lot of
details that are common to adding to a database, but you don't want to be
concerned with coding them every time you add. Encapsulating those details such
that they are accessed through a simpler method (say, Add(T type)) is one way
to achieve good code-reuse
Encapsulation in Java is a mechanism of wrapping the data (variables) and code
acting on the data (methods) together as as single unit.
Abstraction
·
Abstraction is the act
of representing essential features without including the background details or
explanations.
the abstraction principle is used to reduce complexity and allow efficient
design and implementation of complex software systems.
Abstraction is a process process of hiding the implementation details from the
user, only the functionality will be provided to the user. In other words user
will have the information on what the object does instead of how it does it
Static & Dynamic
Binding
·
Static - binding
occurs at compile time
Dynamic - binding occurs at runtime
MVC
·
Model - part of the
application that handles logic for the data we are presenting
View - part of the application that handles display of data
Controller - part of the application that handles user interaction
This process allows you to break up complex applications & focus on one
aspect at a time
CRUD
·
-Create
-Read
-Update
-Delete
Create Table
·
CREATE TABLE person(
id INTEGER PRIMARY KEY,
name TEXT,
age INTEGER);
Insert
·
INSERT INTO
person(id,name,age) VALUES(1,"dylan", 21);
INSERT OR REPLACE INTO..
Select
·
SELECT * FROM person;
SELECT name, age FROM person;
SELECT name, age FROM person WHERE dead=0;
Select from multiple
tables
·
SELECT pet.id,
pet.name, FROM pet, person WHERE pet.id = person.id;
Select (conditions)
·
SELECT DISTINCT genre
FROM movies;
SELECT * FROM movies WHERE name LIKE 'a%';
SELECT * FROM movies ORDER BY rating DESC LIMIT 3;
SELECT * FROM movies ORDER BY rating ASC LIMIT 3;
SELECT SUM(movies) FROM movies;
SELECT MIN/MAX(movies) FROM movies;
Alter
·
ALTER TABLE thing ADD
COLUMN name TEXT;
ALTER TABLE thing DROP COLUMN name;
ALTER TABLE person RENAME TO persons;
Delete
·
DELETE FROM pet WHERE
dead=1;
BigO Notation
·
allows us to say how
the size of inputs affect the runtime of a program
BigO
·
O(1) - constant
O(log n) - logarithmic
O(n) - linear
O(n log n) -
O(n^2) - quadratic
O(2^n) - exponential
O(n!) - factorial
Left Join
·
SELECT * FROM table1
LEFT JOIN table2 on table1.id=table2.id;
Right Join
·
SELECT * FROM table1
RIGHT JOIN table2 on table1.id=table2.id;
Inner Join
·
SELECT * FROM table1
INNER JOIN table2 on table1.id=table2.id;
Outer Join
·
SELECT * FROM table1
FULL OUTER JOIN table2 on table1.id=table2.id;
FizzBuzz
·
public int
fizzBuzz(int n){
if ((n%3==0) && (n%5==0)){
System.out.print("FizzBuzz");
}else if (n%3==0){
System.out.print("Fizz");
}else if (n%5==0){
System.out.print("Buzz");
}else{
System.out.print(n);
}
}
Find pairs of elements
in Array whose sum==a given number
·
public void
findPairs(int input[], int num){
for(i=0; i<input.length; i++){
for(j=i+1; j<input.length; j++){
if(input[i]+input[j]==num){
return input[i], input[j];
}
}
Fibonacci
·
public int
fibonacci(int n){
if(n==0){
return 0;
}else if(n==1){
return 1;
}else{
return fibonacci(n-1) + fibonacci(n-2);
}
}
Find two max numbers
in an array
·
public void
maxNumbers(int input[]){
int maxOne, maxTwo;
for(int i =0; i<input.length; i++){
if(maxOne < input[n]){
maxTwo = maxOne;
maxOne = input[n];
}else if(maxTwo < n){
maxTwo = input[n];
}
return maxOne, maxTwo;
}
------------------------------------------------
for(int n : input){
if(max<n){
maxTwo= maxOne;
maxOne = n;
}else if (maxTwo<n){
maxTwo = n;
}
Reverse a number
·
public int
reverseNum(int n){
int result = 0;
int rem = 0;
while(n>0){
rem = n%10;
n = n/10;
result = result * 10 + rem;
return result;
}
}
Find common elements
between two arrays
·
public void
commonElements(int arr1[], int arr2[]){
HashSet<String> set = new Hashset<String>();
for(int i =0; i<arr1.length; i++){
for(int j =0; j<arr2.length; j++){
if(arr1[i]==arr2[j]){
set.add(arr1[i]);
}
}
return set;
}
}
Reverse a string
·
public class
StringReverse{
String reverse = "";
public String reverseString(String str){
if(str.length==1){
return str;
}else{
reverse += str.charAt(str.length-1) + reverseString(str.substring(0,
str.length-1));
}
return reverse;
}
}
Duplicate in array
·
public void
duplicateCase(int input[]){
Hashset<String> set = new Hashset<String>();
for(int n: input){
if(!set.add(n)){
System.out.print(n);
}
}
}
Factorial
·
public int
factorial(int n){
if(n==1){
return 1;
}else{
return n * factorial(n-1);
}
}
Abstract Class
·
A common use of
abstract classes is to provide an outline of a class similar like an interface
does. But unlike an interface it can already provide functionality, i.e. some
parts of the class are implemented and some parts are just outlined with a
method declaration. ("abstract")
http://stackoverflow.com/questions/1320745/abstract-class-in-java
A class must be declared abstract when it has one or more abstract methods. A
method is declared abstract when it has a method heading, but no body - which
means that an abstract method has no implementation code inside curly braces
like normal methods do.
Abstract class vs
interface
·
class that implements
interface must implement all the method headings listed in interface definition
http://www.javatpoint.com/difference-between-abstract-class-and-interface
Stack
·
http://www.tutorialspoint.com/java/java_stack_class.htm
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