how to find the IP address ie IPv4 address is valid or invalid

package main.java;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;

public class Sample {
public static void main(String args[]) throws IOException {
String IP = "null";
boolean length_flag = true, start_end_flag = true, dot_flag = true, alphaFlag = false;
int dot_counter = 0;
System.out.println("Enter the IP Address");
BufferedReader br = new BufferedReader((new InputStreamReader(System.in)));
IP = br.readLine();
char[] ch = new char[IP.length()];
// Copy character by character into array
for (int i = 0; i < IP.length(); i++) {
ch[i] = IP.charAt(i);
}
//Check the number of characters is more than 15 digits
if(IP.length()>15){
length_flag = false;
}
//Check with the number of dot present in the IP address
if(IP.startsWith(".")||IP.endsWith("."))
{
start_end_flag = false;
}
//Count the number of dot values present in the Input address
for(int i=0; i< IP.length();i++){
if(ch[i]=='.'){
dot_counter++;
}
}
//Check the number of dot present in the ip addres
if(dot_counter != 3)
{
dot_flag = false;
}
//Check any alphabets present in the ip address
for(int i=0;i if ((ch[i] >= 'a' && ch[i] <= 'z') || (ch[i] >= 'A' && ch[i] <= 'Z')) {
alphaFlag = true;
}
}
//If any of the flag is set then make the address as valid IP otherwise mark as Invalid IP
if(length_flag&&start_end_flag&&dot_flag&&(!alphaFlag))
{
System.out.println("Valid IP");
}
else
{
System.out.println("Invalid IP");
}
}
}