Binary to Decimal conversion in Java

This tutorial would help in learning the following:

• Conversion of numbers from binary-system (0 and 1) to decimal-system (using 0 to 9) in Java.
• Re-conversion of characters into their respective ASCII codes
• Code for Binary to Decimal conversion in JAVA

The decimal number system uses all the 10 digits (0 to 9) to represent a number while the binary number system 0 and 1. The following algorithm is used to convert a binary-number to a decimal-number:

let the binary number be 111111

1. Give proper index to each digit of the binary number, starting with zero and from the rightmost digit
   number->111111
   index—->543210
2. multiply the number present at index ‘i’ with the i^th power of  2
   index 0 -> 1* 2⁰ = 1
   index 1 -> 1* 2¹ = 2
   index 2 -> 1* 2² = 4
   index 3 -> 1* 2³ = 8
   index 4 -> 1* 2⁴ = 16
   index 5 -> 1* 2⁵ = 32
3. add all the products obtained from step 2, to get the equivalent decimal number
   1 + 2 + 4 + 8 + 16 + 32 = 63
   (111111)₂ ~ (63)₁₀

Each character used in computing is assigned a special ASCII code (decimal-number-system); hence, once a binary code is converted to its equivalent decimal-number code, the latter can be assigned a character as per the ASCII convention.
Note, there can be different encoding systems on different machines.

Java program to convert binary to decimal

//This program follows the convention of giving a fullstop after the code for an individual character
public class BinaryDeconversion
{
String binarycode;
BinaryDeconversion()//default constructor
{
    binarycode="1000011.1101111.1100100.1100101.100000.1010011.1110000.1100101.1100101.1100100.1111001.";
}
BinaryDeconversion(String x)//parameterized constructor
{
    binarycode=x;
}
public static void main(String args[])
 {
     BinaryDeconversion ob;
    try{//considering the command line argument of the user as the string to be re-converted from binary format
        ob=new BinaryDeconversion(args[0]);
    }//going with the default string in case of any exceptions with the command line argument
     catch(Exception e){ob=new BinaryDeconversion();};
     System.out.print("The decoded value of binary code "+ob.binarycode+" is: ");
     ob.binaryToString(ob.binarycode);
 }
char binary(char array[])
{
    int code=0;
    int temporary;
    int i;
    int j=0;
    for(i=0;array[i]!='\0';i++);//obtaining the index of the last code-character in array[]
    for(--i;i>=0;i--){
        temporary = ((int)array[i]) - ((int)('0'));
        code+=temporary*(int)(Math.pow(2,j++));//Math.pow() helps in giving the required power of 2
    }
    return (char)code;//returning the character corresponding to the integer-code whose value is in 'code'
}
void binaryToString(String code)
{
    char helper[]=new char[10+1];//assuming that the length of binary code for one character will not exceed 10
    int index = 0;
    for(int i=0;i<code.length();i++){
        if(code.charAt(i)=='.')//printing the value of the code for one character
        {
            helper[index]='\0';
            System.out.print(binary(helper));
            index=0;
        }
        else//stacking up the incomplete code for one character
        {
            helper[index++]=code.charAt(i);
        }
    }
}
}//class ends

Output (without command line argument):

The decoded value of binary code 1000011.1101111.1100100.1100101.100000.1010011.1110000.1100101.1100101.1100100.1111001. is: Code Speedy

Summary:

char binary(char[]):

• the index of the last character in array[] is stored in ‘i’
• the value of ‘j’ corresponds with the required power of 2 that is required for the character at given index ‘i’
• the numerical value of the character-code at index ‘i’ is stored in ‘temporary’
• the sum of products for different indices is stored in ‘code’
• the character corresponding to the value of ‘code’ is returned

void binaryToString(String)

• helper[] stores the binary code for one character at a time
• binary(char[]) is called and helper[] is passed to it to print the corresponding character for the binary code in helper[]

Also read:

• Java program to convert Decimal into Hexadecimal