import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegexDemo1
{
    public static void main(String[] args)
    {
        /*
         * . represents single character
         *
         * Parameters:
         * 
         * regex - The expression to be compiled
         * 
         * Returns:
         * 
         * the given regular expression compiled into a pattern
         */
        Pattern pattern = Pattern.compile(".r");
        /*
         * Parameters: 
         * 
         * input - The character sequence to be matched
         * 
         * Returns: 
         * 
         * A new matcher for this pattern
         * 
         */
        Matcher matcher = pattern.matcher("br");
        /*
         * Returns:true if, and only if, the entire region sequence
         * matches this matcher's pattern
         */
        boolean result = matcher.matches();
        System.out.println(result);
    }

}

true

import java.util.regex.Pattern;

public class RegexDemo2
{
    public static void main(String[] args)
    {
        boolean result=Pattern.compile(".r").matcher("ar").matches();  
        System.out.println(result);
    }

}

true

import java.util.regex.Pattern;

/**
 * boolean java.util.regex.Pattern.matches(String regex, CharSequence
 * input)
 * 
 * Compiles the given regular expression and attempts to match the
 * given input against it
 */
public class RegexDemo3
{
    public static void main(String[] args)
    {
        /*
         * Parameters:
         * 
         * regex: The expression to be compiled
         * 
         * input: The character sequence to be matched
         * 
         * Returns:
         * 
         * whether or not the regular expression matches on
         * the input
         */
        boolean result = Pattern.matches(".r", "ar");
        System.out.println(result);
    }

}

true