Alternative to create a new method in a String object?

Question

I have the following situation: I have a txt file of defined positions (type CSV, CNAB, etc) to process and extract values. For the purposes of understanding, follow the code I made and it’s working perfectly:

public class Extract {

    final int[] CPF = new int[]{0, 10};
    final int[] NOME = new int[]{15, 45};

    public static void main(String args[]) {

      FileInputStream fis = new FileInputStream("C:\\cnab.txt");        
      String line;

      while ((line = fis.readLine()) != null) {
          System.out.println(getValue(line, CPF));
          System.out.println(getValue(line, NOME)); 
      }
    }

    private String getValue(String line, int[] slice) {
        return line.substring(slice[0], slice[1]);
    }
 }

So far ok, but I’d like something more readable, elegant, such as:

System.out.println(line.getValue(CPF));

But we all know that String is final. Does anyone have any suggestions?

Answer 1

Why shouldn’t you do it

Changing a basic language class (whatever) to implement a simple requirement like this is a big mistake.

The Java language purposely prevents for security reasons that basic types like String and Integer are modified or extended with inheritance. Such classes are declared with the modifier final.

One of the great dangers of this is in relation to organization. Programmers would start making several language modifications, include libraries that would make other modifications and the code would end up a big mess.

Another problem is performance. Large systems would end up with too much overloading of additional methods and subclasses where simply not needed.

Ever wondered if each programmer tried to modify the class String to meet your immediate needs?

Do O right

Inheritance or modification of existing classes nay is the best solution from the point of view of design object-oriented to situations like this.

In this case, you can simply encapsulate the line into a new object containing the method you need.

Example:

public class LinhaArquivo {
    private String linha;
    public LinhaArquivo(String linha) { 
        this.linha = linha;
    }
    public String getValue(int[] slice) {
        return linha.substring(slice[0], slice[1]);
    }
}

Then you could change your code as follows:

public class Extract {

    final int[] CPF = new int[]{0, 10};
    final int[] NOME = new int[]{15, 45};

    public static void main(String args[]) {

      FileInputStream fis = new FileInputStream("C:\\cnab.txt");        
      String line;

      while ((line = br.readLine()) != null) {
          LinhaArquivo linha = new LinhaArquivo(line);
          System.out.println(linha.getValue(CPF));
          System.out.println(linha.getValue(NOME)); 
      }
    }

}

Answer 2

If positions are static, create an Enum

public enum ArchiveEnum {

NOME(0, 5),
CPF(6, 20);
private Integer minAge;
private Integer maxAge;

private ArchiveEnum(Integer minAge, Integer maxAge) {
    this.minAge = minAge;
    this.maxAge = maxAge;
}

public Integer getMinAge() {
    return minAge;
}

public void setMinAge(Integer minAge) {
    this.minAge = minAge;
}

public Integer getMaxAge() {
    return maxAge;
}

public void setMaxAge(Integer maxAge) {
    this.maxAge = maxAge;
}
}

And in your method, pass the type of ENUM

public String getCampo(ArchiveEnum enumValue) {
    String archive = "TIAGO,111.111.111-11"; // Suposição de linha do arquivo
    return archive.subString(enumValue.getMinAge(), enumValue.getMaxAge()).toString();
}