Find the address class and address type from the IP address with Java


The following information is displayed from the IP address specified by the argument (only one). ・ Address class (class A or class B or class C or class D) -Global IP address or private IP address

It is uploaded on GitHub. → ipAddressInfo I haven't tested it so much, so there may be miscoding ... If you find something wrong with the code or an improvement, please let us know in the comments or edit request.


package pk;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class Main {

	private static final String CLASS_A_PREFIX = "0";
	private static final String CLASS_B_PREFIX = "10";
	private static final String CLASS_C_PREFIX = "110";
	private static final String CLASS_D_PREFIX = "1110";

	public static void main(String[] args) {
		//Argument check
		if (args.length != 1) {
			System.out.println("Specify the IP address in the argument.");

		//Regular expression for IP address determination
		Pattern pattern = Pattern.compile(
		Matcher matcher = pattern.matcher(args[0]);

		if (matcher.find()) {
			List<String> addressList = new ArrayList<>();
			addressList = Arrays.asList(args[0].split("\\."));
			String addressClass = getIpAdressClass(getBinaryAddress(addressList.get(0)));

			switch (addressClass) {
				case CLASS_A_PREFIX:
					if (isPrivateAddress(addressList, CLASS_A_PREFIX)) {
						showResult("Class A", "Private IP address");
					} else {
						showResult("Class A", "Global IP address");
				case CLASS_B_PREFIX:
					if (isPrivateAddress(addressList, CLASS_B_PREFIX)) {
						showResult("Class B", "Private IP address");
					} else {
						showResult("Class B", "Global IP address");
				case CLASS_C_PREFIX:
					if (isPrivateAddress(addressList, CLASS_C_PREFIX)) {
						showResult("Class C", "Private IP address");
					} else {
						showResult("Class C", "Global IP address");
				case CLASS_D_PREFIX:
					System.out.println("Class D.");
					System.out.println("An address that does not belong to any class.");
		} else {
			System.out.println("It does not follow the IP address format.");

	 *Convert from decimal to binary
	 * @param decimalAddress Decimal address
	 * @return Decimal number converted to binary number
	private static String getBinaryAddress(String decimalAddress) {
		return String.format("%8s", Integer.toBinaryString(Integer.valueOf(decimalAddress))).replace(" ", "0");

	 *Determine which class it belongs to
	 * @param binaryAddress Binary address
	 * @Prefix for each return class, if it does not belong to any class"1"return it
	private static String getIpAdressClass(String binaryAddress) {
		if (CLASS_A_PREFIX.equals(binaryAddress.substring(0, 1))) {
			return CLASS_A_PREFIX;
		} else if (CLASS_B_PREFIX.equals(binaryAddress.substring(0, 2))) {
			return CLASS_B_PREFIX;
		} else if (CLASS_C_PREFIX.equals(binaryAddress.substring(0, 3))) {
			return CLASS_C_PREFIX;
		} else if (CLASS_D_PREFIX.equals(binaryAddress.substring(0, 4))) {
			return CLASS_D_PREFIX;
		} else {
			return "1";

	 *Determine whether the IP address belonging to the address class from class A to class C is a global IP or a private IP
	 * @param classPrefix
	 * @return Returns true for private IP addresses, false otherwise
	private static boolean isPrivateAddress(List<String> addressList, String classPrefix) {
		int firstSet = Integer.valueOf(addressList.get(0));
		int secondSet = Integer.valueOf(addressList.get(1));

		switch (classPrefix) {
				//The range of class A private IP addresses is
				// ~
				if (firstSet == 10) {
					return true;
				//The range of class B private IP addresses is
				// ~
				if (firstSet == 172 && (16 <= secondSet && secondSet <= 31)) {
					return true;
				//The range of class C private IP addresses is
				// ~
				if (firstSet == 192 && secondSet == 168) {
					return true;
				//Class D is for multicast, so there is no concept of global or private
				return false;
		return false;

	 *Display the IP address identification result
	 * @param addressClass IP address class name
	 * @param addressStatus Global IP address or private IP address
	private static void showResult(String addressClass, String addressStatus) {
		System.out.println(addressClass + "And" + addressStatus + "is.");

[Execution example]

> java pk.Main
Class C and global IP address.


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[Bonus corner]

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