Validity checking in Java-CodePudding

First off, I am extremely new to coding and I need an answer to this urgently. I am asked to create an array or arraylist of objects using my class that requires a "Validity checking component for the input of each attribute entered. Such checking requires the use of at least one loop and an if-else structure." I have no idea how to make this and I am extremely confused about what it's asking me. My code so far looks like this:

import java.util.ArrayList;

public class AList {

public static void main(String[] args)
{
    Author a1 = new Author("Stephen King", "[email protected]", "Male", "74","It","The Body");
    Author a2 = new Author("Neil Gaiman", "N/A", "Male","61","Coraline","Eternals");
    Author a3 = new Author("Margaret Atwood", "N/A","Female","82","The Handmaid's Tale","Cat's Eye");

    ArrayList<Author> author1 = new ArrayList<>();
    author1.add(a1);
    System.out.println(author1.get(0).name);
    System.out.println(author1.get(0).email);
    System.out.println(author1.get(0).gender);
    System.out.println(author1.get(0).age);
    System.out.println(author1.get(0).favBook);
    System.out.println(author1.get(0).underBook);
    System.out.println("*************************");

    ArrayList<Author> author2 = new ArrayList<>();
    author2.add(a2);
    System.out.println(author2.get(0).name);
    System.out.println(author2.get(0).email);
    System.out.println(author2.get(0).gender);
    System.out.println(author2.get(0).age);
    System.out.println(author2.get(0).favBook);
    System.out.println(author2.get(0).underBook);
    System.out.println("*************************");

    ArrayList<Author> author3 = new ArrayList<>();
    author3.add(a3);
    System.out.println(author3.get(0).name);
    System.out.println(author3.get(0).email);
    System.out.println(author3.get(0).gender);
    System.out.println(author3.get(0).age);
    System.out.println(author3.get(0).favBook);
    System.out.println(author3.get(0).underBook);
    System.out.println("*************************");


}

public static class Author{

    private String name;
    private String email;
    private final String gender;
    private final String age;
    private final String favBook;
    private final String underBook;

    public Author(String name, String email, String gender, String AGE, String FavBook, String UnderBook) {
        this.name = name;
        this.email = email;
        this.gender = gender;
        this.age = AGE;
        this.favBook = FavBook;
        this.underBook = UnderBook;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    public String getName() {
        return this.name;
    }
    public String getEmail() {
        return this.email;
    }
    public String getGender() {
        return this.gender;
    }
    public String getAge() {
        return this.age;
    }
    public String getFavBook() {
        return this.favBook;
    }
    public String getUnderBook() {
        return this.underBook;
    }

}





    }

Also, another component to this code that I have to complete is "Files with being used to load and save array/ArrayList objects from a text file (.txt extension using Tab Separated Values format.)" which I also have no idea how to do. I am so confused and I really need help! How do I go about completing all of this?

CodePudding user response：

Take out the validation logic in separate method

public Map<String,String> validate(Author author) { 
    Map<String,String>errors= new HashMap();
    String name = auth.getName();
    if(name==null || name.isEmpty(){
       errors.put("name","Name is required");
    }
}

For reading files, you can use BufferedReader. Use readLine() method to read a row from file, use String classes split method to split it on tab separator

CodePudding user response：

I'm not really sure what is required for an object to be "valid" in your context. However, I can help with the second part. You can use a PrintWriter to print to a file, and "\t" to print a tab. You can see what Tab Separated Values is from https://en.wikipedia.org/wiki/Tab-separated_values.

PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter("file.txt")));

use this statement to print an Author's variables in Tab separated values format:

pw.println(a1.name   "\t"   a1.email   "\t"   a1.gender   "\t"   a1.age   "\t"   a1.favBook   "\t"   a1.underBook);

Make sure to call pw.close() after you are done writing.

To parse all Author objects from a text file, you can use a Bufferedreader:

BufferedReader br = new BufferedReader(new FileReader("file.txt"));
ArrayList<Author> authors = new ArrayList<>();
String input = br.readLine();
while(input != null){
    String[] in = input.split("\t");
    authors.add(new Author(in[0], in[1], in[2], in[3], in[4], in[5]));
    input = br.readLine();
}

the String.split() method will split the string into several Strings. In this case, it will split the String at every location where there is a tab, or "\t".

Using BufferedReader will throw an error, but if you add "throws IOException" right after the method name and right before the parenthesis, it will work.

public static void main(String[] args) throws IOException {...

Another suggestion I have is that when you print the variables of an Author, you don't need to add them to an ArrayList, you can directly print them.