Perctapera patch 1

Algorithms/QuickSort.java

@@ -0,0 +1,54 @@
+import java.util.*;
+
+class QuickSort { 
+    //selects last element as pivot, pi using which array is partitioned. 
+    int partition(int intArray[], int low, int high) { 
+        int pi = intArray[high];  
+        int i = (low-1); // smaller element index   
+        for (int j=low; j<high; j++) { 
+            // check if current element is less than or equal to pi 
+            if (intArray[j] <= pi) { 
+                i++; 
+                // swap intArray[i] and intArray[j] 
+                int temp = intArray[i]; 
+                intArray[i] = intArray[j]; 
+                intArray[j] = temp; 
+            } 
+        } 
+
+        // swap intArray[i+1] and intArray[high] (or pi) 
+        int temp = intArray[i+1]; 
+        intArray[i+1] = intArray[high]; 
+        intArray[high] = temp; 
+
+        return i+1; 
+    } 
+
+
+  //routine to sort the array partitions recursively
+    void quick_sort(int intArray[], int low, int high) { 
+        if (low < high) { 
+            //partition the array around pi=>partitioning index and return pi
+            int pi = partition(intArray, low, high); 
+
+            // sort each partition recursively 
+            quick_sort(intArray, low, pi-1); 
+            quick_sort(intArray, pi+1, high); 
+        } 
+    } 
+}
+
+class Main{
+    public static void main(String args[]) {
+        //initialize a numeric array, intArray
+        int intArray[] = {4,-1,6,8,0,5,-3}; 
+        int n = intArray.length; 
+        //print the original array
+        System.out.println("Original Array: " + Arrays.toString(intArray));
+        //call quick_sort routine using QuickSort object
+        QuickSort obj = new QuickSort(); 
+        obj.quick_sort(intArray, 0, n-1); 
+        //print the sorted array
+        System.out.println("\nSorted Array: " + Arrays.toString(intArray)); 
+    } 
+}

Design Patterns/SingleObject.java

@@ -0,0 +1,18 @@
+public class SingleObject {
+
+   //create an object of SingleObject
+   private static SingleObject instance = new SingleObject();
+
+   //make the constructor private so that this class cannot be
+   //instantiated
+   private SingleObject(){}
+
+   //Get the only object available
+   public static SingleObject getInstance(){
+      return instance;
+   }
+
+   public void showMessage(){
+      System.out.println("Hello World!");
+   }
+}

Design Patterns/SingletonPatternDemo.java

@@ -0,0 +1,14 @@
+public class SingletonPatternDemo {
+   public static void main(String[] args) {
+
+      //illegal construct
+      //Compile Time Error: The constructor SingleObject() is not visible
+      //SingleObject object = new SingleObject();
+
+      //Get the only object available
+      SingleObject object = SingleObject.getInstance();
+
+      //show the message
+      object.showMessage();
+   }
+}

Documentation/OOPS.md

@@ -152,6 +152,25 @@ accessible within same class and package within which its class is defined.
 * `Method body:` it is enclosed between braces. The code you need to be executed to perform your intended operations.
 
 
+## An exception (or exceptional event) is a problem that arises during the execution of a program. When an Exception occurs the normal flow of the program is disrupted and the program/Application terminates abnormally, which is not recommended, therefore, these exceptions are to be handled.
+
+** An exception can occur for many different reasons. Following are some scenarios where an exception occurs.**
+
+* A user has entered an invalid data.
+
+* A file that needs to be opened cannot be found.
+
+* A network connection has been lost in the middle of communications or the JVM has run out of memory.
+
+* Some of these exceptions are caused by user error, others by programmer error, and others by physical resources that have failed in some manner.
+
+* Based on these, we have three categories of Exceptions. You need to understand them to know how exception handling works in Java.
+
+* Checked exceptions − A checked exception is an exception that is checked (notified) by the compiler at compilation-time, these are also called as compile time exceptions. These exceptions cannot simply be ignored, the programmer should take care of (handle) these exceptions.
+
+* Unchecked exceptions − An unchecked exception is an exception that occurs at the time of execution. These are also called as Runtime Exceptions. These include programming bugs, such as logic errors or improper use of an API. Runtime exceptions are ignored at the time of compilation.
+
+* Errors − These are not exceptions at all, but problems that arise beyond the control of the user or the programmer. Errors are typically ignored in your code because you can rarely do anything about an error. For example, if a stack overflow occurs, an error will arise. They are also ignored at the time of compilation.
 
 
 

Examples/Recursion.java

@@ -0,0 +1,20 @@
+class HelloWorld{
+
+  public static void main(String[] args){
+
+  static int fact(int n)
+    {
+        if (n == 1)
+
+		// base condition
+            return 1;
+        else   
+            return n*fact(n-1);    
+    }    
+	public static void main(String[] args) {
+    int result = fact(10);
+
+     System.out.println("10! = " + result);
+    }
+  }
+}