Java – Constructor vs setter validations

java

I have the following class : 

public class Project {

    private int id;
    private String name;  

    public Project(int id, String name, Date creationDate, int fps, List<String> frames) {
        if(name == null ){
            throw new NullPointerException("Name can't be null");
        }

        if(id == 0 ){
            throw new IllegalArgumentException("id can't be zero");
        }

            this.name = name;
            this.id = id;

    }

    private Project(){}

    public int getId() {
        return id;
    }

    public void setId(int id) { 
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

I have three questions:

  1. Do I use the class setters instead of setting the fields directly. One of the reason that I set it directly, is that in the code the setters are not final and they could be overridden.

  2. If the right way is to set it directly and I want to make sure that the name filed is not null always. Should I provide two checks, one in the constructor and one in the setter.

  3. I read in effective java that I should use NullPointerException for null parameters. Should I use IllegalArgumentException for other checks, like id in the example.

Best Answer

Your class allows someone to say myProject.setName(null), avoiding the null check in the constructor. If you want to set stuff through the constructor but need checks (question 2), I suggest doing the checks in set-methods and call those from the constructor. Example:

public class Project {

    private int id;
    private String name;  

    public Project(int id, String name, Date creationDate, int fps, List<String> frames) {
        setName(name);
        setId(id);
    }

    public void setId(int id) { 
        if(id == 0 ){
            throw new IllegalArgumentException("id can't be zero");
        }
        this.id = id;
    }

    public void setName(String name) {
        if(name == null ){
            throw new NullPointerException("Name can't be null");
        }
        this.name = name;
    }

}

This avoids code duplication.

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