Convert a binary string to decimal in Java

This post will discuss how to convert a binary string to decimal in Java.

1. Using `Integer.parseInt()` method

To convert a base 2 string to a base 10 integer, you can use the overloaded version of the Integer#parseInt() method, which allows you to specify the radix. Following is a simple example demonstrating its usage to parse a string as a signed integer in the specified radix.

public class Main

{

public static void main(String[] args)

{

String binary = "11111111";

int i = Integer.parseInt(binary, 2);

System.out.println(i); // 255

}

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The maximum value of a signed integer is 2³¹-1, which is equivalent to 01111111 11111111 11111111 11111111 in binary. This is demonstrated below:

public class Main

{

public static void main(String[] args)

{

String binary = "01111111111111111111111111111111";

int i = Integer.parseInt(binary, 2);

System.out.println(i); // 2147483647

}

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If you need to convert the binary string 11111111 11111111 11111111 11111111 to corresponding decimal value -1, the above method won’t work. To convert -1 from binary to decimal, you may want to use the Long.parseLong() method, as shown below:

public class Main

{

public static void main(String[] args)

{

String binary = "11111111111111111111111111111111";

int i = (int) Long.parseLong(binary, 2);

System.out.println(i); // -1

}

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Alternatively, you can also use the Integer.parseUnsignedInt() method to convert the binary string 11111111 11111111 11111111 11111111 to a decimal value.

public class Main

{

public static void main(String[] args)

{

String binary = "11111111111111111111111111111111";

int i = Integer.parseUnsignedInt(binary, 2);

System.out.println(i); // -1

}

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2. Using Custom Routine

You can even write a custom routine for this simple task. Here’s how the code would look like:

public class Main

{

public static int toInteger(String binary) {

long decimal = 0;

for (int i = binary.length() - 1; i >= 0; i--) {

if (binary.charAt(i) == '1') {

decimal += Math.pow(2, (binary.length() - i - 1));

}

return (int)decimal;

}

public static void main(String[] args) {

String binary = "11111111111111111111111111111111";

int i = toInteger(binary);

System.out.println(i); // -1

}

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That’s all about converting a binary string to decimal in Java.

Convert a binary string to decimal in Java

1. Using Integer.parseInt() method

2. Using Custom Routine

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1. Using `Integer.parseInt()` method