import java.util.*;
import java.lang.*;
import java.io.*;
 
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		String r10to99 = "[1-9][0-9]"; //numbers from 10 to 99
		String r100to199 = "1[0-9][0-9]"; //numbers from 100 to 199
		String r200to255 = "2[0-4][0-9]|25[0-5]"; //numbers from 200 to 255
 
		//combine all - numbers from 0 to 255   
		String r0to255 = "(?:[0-9]|" + r10to99 + "|" + r100to199 + "|" + r200to255 + ")"; 
 
		String regexIP = r0to255 + "(?:[.]" + r0to255 + "){3}"; 
 
		System.out.println("15.15.15.15".matches(regexIP)); // true
		System.out.println("15".matches(regexIP)); // false
	}
}

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