Java – Convert Integer to Binary
In Java, we can use Integer.toBinaryString(int)
to convert an Integer to a binary string representative.
public final class Integer extends Number
implements Comparable<Integer>, Constable, ConstantDesc {
public static String toBinaryString(int i) {
return toUnsignedString0(i, 1);
}
//...
}
This article will show you two methods to convert an Integer to a binary string representative.
- JDK
Integer.toBinaryString
. - Old school bit masking technique.
1. Convert Int to Binary Integer.toBinaryString
1.1 This Java example tries to convert an int
to a binary string representation.
int input = 10;
String result = Integer.toBinaryString(input);
System.out.println(result); // 1010
Output
1010
1.2 The output of the Integer.toBinaryString
is a lack of zero paddings, and we can use String.Format
and replaceAll
to improve or pretty print a binary string.
int input = 10;
String result = Integer.toBinaryString(input);
String resultWithPadding = String.format("%32s", result).replaceAll(" ", "0"); // 32-bit Integer
System.out.println(resultWithPadding);
Output
00000000000000000000000000001010
1.3 This Java example further improves the binary format with a separator.
package com.mkyong.crypto.bytes;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
public class IntToBinaryExample1 {
public static void main(String[] args) {
int input = 10;
String result = Integer.toBinaryString(input);
String resultWithPadding = String.format("%32s", result).replaceAll(" ", "0");
System.out.println(resultWithPadding);
System.out.println(printBinary(resultWithPadding, 8, " | ")); // 00000000 | 00000000 | 00000000 | 00001010
System.out.println(printBinary(resultWithPadding, 4, " ")); // 0000 0000 0000 0000 0000 0000 0000 1010
}
public static String printBinary(String binary, int blockSize, String separator) {
List<String> result = new ArrayList<>();
int index = 0;
while (index < binary.length()) {
result.add(binary.substring(index, Math.min(index + blockSize, binary.length())));
index += blockSize;
}
return result.stream().collect(Collectors.joining(separator));
}
}
Output
00000000000000000000000000001010
00000000 | 00000000 | 00000000 | 00001010
0000 0000 0000 0000 0000 0000 0000 1010
2. Convert Int to Binary (Bit Masking)
2.1 This Java example uses bit masking to generate a binary string from an integer.
StringBuilder result = new StringBuilder();
for (int i = 31; i >= 0; i--) {
int mask = 1 << i;
result.append((number & mask) != 0 ? "1" : "0");
}
In Bitwise AND operation, only 1 & 1
is 1
.
1 & 1 = 1
1 & 0 = 0
0 & 1 = 0
0 & 0 = 0
2.2 For example, int 10
a 32-bit integer, internally, computer see it as 0000 1010
. The idea is we loop 32 times, and each time creates a new 32-bit int 1 << loop - 1
, and performs a bitwise AND with the int 10
, if the result is not equal zero, append one else append zero.
See the following patterns:
# Each loop will move the bit from the left side to the right side by 1 bit.
# loop 1
00000000 | 00000000 | 00000000 | 00001010 = 10
& = Bitwise AND
10000000 | 00000000 | 00000000 | 00000000 = 1 << 31
=
00000000 | 00000000 | 00000000 | 00000000 = 0 (result)
# loop 2
00000000 | 00000000 | 00000000 | 00001010 = 10
& = Bitwise AND
01000000 | 00000000 | 00000000 | 00000000 = 1 << 30
=
00000000 | 00000000 | 00000000 | 00000000 = 0 (result)
# fast forward...3...28
# loop 29
00000000 | 00000000 | 00000000 | 00001010 = 10
& = Bitwise AND
00000000 | 00000000 | 00000000 | 00001000 = 1 << 3
=
00000000 | 00000000 | 00000000 | 00001000 = 1 (result)
# loop 30
00000000 | 00000000 | 00000000 | 00001010 = 10
& = Bitwise AND
00000000 | 00000000 | 00000000 | 00000100 = 1 << 2
=
00000000 | 00000000 | 00000000 | 00000000 = 0 (result)
# loop 31
00000000 | 00000000 | 00000000 | 00001010 = 10
& = Bitwise AND
00000000 | 00000000 | 00000000 | 00000010 = 1 << 1
=
00000000 | 00000000 | 00000000 | 00000010 = 1 (result)
# loop 32
00000000 | 00000000 | 00000000 | 00001010 = 10
& = Bitwise AND
00000000 | 00000000 | 00000000 | 00000001 = 1 << 0
=
00000000 | 00000000 | 00000000 | 00000000 = 0 (result)
Here’s the full example.
package com.mkyong.crypto.bytes;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
public class IntToBinaryExample2 {
public static void main(String[] args) {
int input = 10;
String result = convertIntToBinaryString(input);
String resultWithPadding = String.format("%32s", result).replaceAll(" ", "0");
System.out.println(printBinary(resultWithPadding, 8, " - "));
}
public static String convertIntToBinaryString(int number) {
StringBuilder result = new StringBuilder();
for (int i = 31; i >= 0; i--) {
int mask = 1 << i;
result.append((number & mask) != 0 ? "1" : "0");
}
return result.toString();
}
public static String printBinary(String binary, int blockSize, String separator) {
List<String> result = new ArrayList<>();
int index = 0;
while (index < binary.length()) {
result.add(binary.substring(index, Math.min(index + blockSize, binary.length())));
index += blockSize;
}
return result.stream().collect(Collectors.joining(separator));
}
}
Output
00000000 - 00000000 - 00000000 - 00001010