java：ArrayList（）方法返回结果：如果传递参数或不传递参数

Question

I want to write the method listCopies() that returns in an ArrayList all copies of a written work in a given language(eg : english); if no language is given (empty string), all copies of the library will be returned (in all languages) . This is the code i have developed but it doesnt work cause in the main(String[] args) {...} it calls 2 times this method , one with the argument passed and in the second without an argument :

public ArrayList<Exemplary> listCopies(String l){
    ArrayList <Exemplary> tmp = new ArrayList<Exemplary>();
    for( int i = 0 ; i < copies.size(); i++){  
                 if(copies.get(i).getWrittenWork().getLanguage().equals(language)){ 
                tmp.add(Ex);
             }
    }
    return (tmp);}

I want to rewrite this code in a way that with or without argument (String lang) > it returns the array tmp .

Answer 1

There's a multitude of problems with your code:

• lang is used on the first line, but further on you use language
• Exemplary is used on the first line, but on the 2nd you use Exemplairy
• the method doesn't have a closing } at the end
• you don't have code that deals with an empty language
• the loop should be rewritten as an enhanced for loop
• the interface List should be used instead of the class ArrayList where possible