I am answering this very late, but this is what really useful for new reader. This is a very simple and efficient way to get random VALID names. To do so, add maven repository in POM.xml

<dependency>
    <groupId>com.github.javafaker</groupId>
    <artifactId>javafaker</artifactId>
    <version>0.12</version>
</dependency>

And then use the Faker class as below in your Java code

Faker faker = new Faker();

String name = faker.name().fullName();
String firstName = faker.name().firstName();
String lastName = faker.name().lastName();

String streetAddress = faker.address().streetAddress();

Try printing the result using standard System.out.println();

For more reference Faker Lib

Consider Regex

Your WordChecker class has numerous helper methods that all bubble up to just pattern matching. This is exactly why Regex exists, Java has Pattern and Matcher classes in java.util.regex that can help you do this fairly succinctly. For example, to check for only vowels or only consonants you can have this:

public class WordChecker {
    private static final Pattern VOWEL_PATTERN = Pattern.compile("^[aeiouy]+$");
    private static final Pattern CONSONANT_PATTERN = Pattern.compile("^[bcdfghjklmnpqrstvwxz]+$");

    private static boolean onlyVowels(String input) {
        return VOWEL_PATTERN.matcher(input).matches();
    }

    private static boolean onlyConsonants(String input) {
        return CONSONANT_PATTERN.matcher(input).matches();
    }
}

Do note, however, that I make these methods static, so call them with WordChecker.onlyVowels("..."); As it stands all the content consists of helper functions independent of any particular implementation so being static fits well.

For further reference look at the documentation here.

Use meaningful names; avoid deceptive names.

Naming things can be surprisingly difficult especially when striving to keep it short and indicate full meaning, yet only returning 0 or 1 seems completely unexpected from a method that is meant to return the similarity between two things (similarity implies a multitude of outputs on a range, the way you apply it here essentially turn it into a boolean).

Leverage the API

One of the premier merits of using any language in particular is the available libraries. Unless this was done as an exercise the majority of the Dictionary class can be eliminated by using a HashMap.

import java.util.*; 

public class characters 
{
    public static void main(String[] args)
    {
       Random generate = new Random();
       String[] name = {"John", "Marcus", "Susan", "Henry"};

       System.out.println("Customer: " + name[generate.nextInt(4)]);      

    }
}

See how easy it is? I gave 4 simple names which can be replaced with words and such. The "4" in the code represents the number of names in the String. This is about as simple as it gets. And for those who want it even shorter(all I did was decrease the spacing):

import java.util.*; 
public class characters{ 
public static void main(String[] args){
Random generate = new Random(); 
String[] name = {"John", "Marcus", "Susan", "Henry"};
System.out.println("Customer: " + name[generate.nextInt(4)]); }}