Fixed multiple typos, and minor syntax issues.

Conversions/DecimalToHexaDecimal.java

@@ -1,33 +1,30 @@
 import java.lang.StringBuilder;
 import java.util.Scanner;
 
-class Test {
-  private static final int sizeOfIntInHalfBytes = 8;
-  private static final int numberOfBitsInAHalfByte = 4;
-  private static final int halfByte = 0x0F;
-  private static final char[] hexDigits = { 
-    '0', '1', '2', '3', '4', '5', '6', '7', 
-    '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
-  };
+class DecimalToHexaDecimal {
+	private static final int sizeOfIntInHalfBytes = 8;
+	private static final int numberOfBitsInAHalfByte = 4;
+	private static final int halfByte = 0x0F;
+	private static final char[] hexDigits = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E',
+			'F' };
 
-  public static String decToHex(int dec) {
-    StringBuilder hexBuilder = new StringBuilder(sizeOfIntInHalfBytes);
-    hexBuilder.setLength(sizeOfIntInHalfBytes);
-    for (int i = sizeOfIntInHalfBytes - 1; i >= 0; --i)
-    {
-      int j = dec & halfByte;
-      hexBuilder.setCharAt(i, hexDigits[j]);
-      dec >>= numberOfBitsInAHalfByte;
-    }
-    return hexBuilder.toString(); 
-  }
+	public static String decToHex(int dec) {
+		StringBuilder hexBuilder = new StringBuilder(sizeOfIntInHalfBytes);
+		hexBuilder.setLength(sizeOfIntInHalfBytes);
+		for (int i = sizeOfIntInHalfBytes - 1; i >= 0; --i) {
+			int j = dec & halfByte;
+			hexBuilder.setCharAt(i, hexDigits[j]);
+			dec >>= numberOfBitsInAHalfByte;
+		}
+		return hexBuilder.toString();
+	}
 
-  public static void main(String[] args) {
-    Scanner sc = new Scanner(System.in);
-      System.out.println("Write your Number to convert into HexaDecimal: ")
-     int dec = 305445566;
-     String hex = Integer.toHexString(dec);
-     String hex = decToHex(dec);
-     System.out.println(hex);       
-  }
+	public static void main(String[] args) {
+		Scanner sc = new Scanner(System.in);
+		System.out.println("Write your Number to convert into HexaDecimal: ");
+		int userInputInt = sc.nextInt();
+		
+		String hex2 = decToHex(userInputInt);
+		System.out.println(hex2);
+	}
 }

Conversions/DecimalToOctal.java

@@ -6,7 +6,7 @@
  * @author Unknown
  *
  */
-class Decimal_Octal
+class DecimalToOctal
 {
 	/**
 	 * Main Method

Conversions/HexaDecimalToBinary.java

@@ -3,7 +3,7 @@
 import java.util.Scanner;
 import javax.swing.*;
 
-public class HexaToBin {
+public class HexaDecimalToBinary {
 
     private final int LONG_BITS = 8;
 
@@ -28,7 +28,7 @@ public static void main(String[] args) {
         //Testing Numbers:
         String[] hexNums = {"1", "A1", "ef", "BA", "AA", "BB",
             "19", "01", "02", "03", "04"};
-        Convert objConvert = new Convert();
+        HexaDecimalToBinary objConvert = new HexaDecimalToBinary();
 
         for (String num : hexNums) {
             objConvert.convert(num);

Conversions/OctalToBinary.java

@@ -1,49 +1,110 @@
+package Conversions;
+
 import java.util.Scanner;
 
 /**
- * Converts any Octal number to a Binary number
  * 
- * @author Zachary Jones
- *
+ * @author Rohit Agarwal
+ * @category Base Conversion
+ * @problem Convert Octal to Binary
+ * 
  */
 public class OctalToBinary {
 
+	public static void main(String[] args) {
+
+		Scanner input = null;
+		try {
+			input = new Scanner(System.in);
+			System.out.println("Enter octal number : ");
+			String number = input.next();
+
+			if (isOctalNumber(number)) {
+				String binary = getBinaryFromOctalNumber(number);
+				System.out.println("Binary Number : " + binary);
+			} else {
+				System.out.println("Please enter valid octal number.");
+			}
+
+		} finally {
+			if (input != null) {
+				input.close();
+			}
+		}
+
+	}
+
 	/**
-	 * Main method
-	 * 
-	 * @param args Command line arguments
+	 * Converts a String to binary
+	 * @param number String number (Octal)
+	 * @return binary String
 	 */
-	public static void main(String args[]) {
-		Scanner sc = new Scanner(System.in);
-		int o = sc.nextInt();
-		System.out.println("Binary equivalent: " + convertOctalToBinary(o));
-		sc.close();
+	private static String getBinaryFromOctalNumber(String number) {
+
+		// Convert Octal to Decimal
+		int decimal = getDecimalFromOctalNumber(number);
+		// Convert Decimal to Binary
+		String binary = getBinaryFromDecimalNumber(decimal);
+		return binary;
 	}
-	
+
 	/**
-	 * This method converts an octal number
-	 * to a binary number.
-	 * 
-	 * @param o The octal number
-	 * @return The binary number
+	 * Converts a Decimal to binary 
+	 * @param decimal
+	 * @return binary String
 	 */
-	public static int convertOctalToBinary(int o) {
-		Scanner scan;
-		int num;
-
-		void getVal() {
-
-			System.out.println("Octal to Binary");
-			scan = new Scanner(System.in);
-			// Entering the needed number
-			System.out.println("\nEnter the number : ");
-			num = Integer.parseInt(scan.nextLine(), 8);
+	private static String getBinaryFromDecimalNumber(int decimal) {
+
+		int remainder = 0;
+		StringBuilder binary = new StringBuilder();
+		while (decimal != 0) {
+			remainder = decimal % 2;
+			// Converting Integer to String and adding into StringBuilder.
+			binary.append(String.valueOf(remainder));
+			decimal = decimal / 2;
 		}
-
-		void convert() {
-
-			String binary = Integer.toBinaryString(num);		
-			System.out.println("Binary Value is : " + binary);
+
+		// Reverse String using library function of StringBuilder class.
+		return binary.reverse().toString();
+	}
+
+	/**
+	 * Converts Octal to Decimal
+	 * @param number
+	 * @return sum
+	 */
+	private static int getDecimalFromOctalNumber(String number) {
+
+		// Converting String to StringBuilder.
+		StringBuilder string = new StringBuilder(number);
+		string = string.reverse();
+		int length = string.length();
+		int digit, power, sum = 0;
+		for (int i = 0; i < length; i++) {
+			digit = string.charAt(i) - 48;
+			power = (int) Math.pow(8, i);
+			sum = sum + digit * power;
 		}
+		return sum;
 	}
+
+	/**
+	 * Checks that the String contains digits 0-7
+	 * @param number Input string
+	 * @return result
+	 */
+	private static boolean isOctalNumber(String number) {
+
+		/*
+		 * Regular expression that matches string containing only octal
+		 * digits[0-7].
+		 */
+		String pattern = "^[0-7]+$";
+		boolean result = false;
+		if (number.matches(pattern)) {
+			result = true;
+		}
+		return result;
+	}
+
 }