CODEWITHSUNDEEP
javafinal
dnc253
dnc253

Reputation: 40337

Java - Any way to make variable unmodifiable after being set in the constructor?

I have a member variable that in a class that I want to make sure nothing changes it after it is set in the constructor. So, it would look something like this:

public class MyClass
{
    private String myVar = null;

    public MyClass(DataObj dataObj)
    {
        myVar = dataObj.getFinalVarValue();
        //at this point I don't want anything to be able change the value of myVar
    }

    ....
}

My first thought was to see I could just add the final modifier to the variable, but the compiler complains about assigning a value to the final field. Is it possible to accomplish this?

Upvotes: 3

Views: 1660

Answers (3)

iozee
iozee

Reputation: 1349

String objects are already immutable. So adding the private final modificator is enough.

Upvotes: -1

MartinK
MartinK

Reputation: 1938

The compiler complains (in the constructor), because you already provide an initialization by writing

private String myVar = null;

remove the '= null' part. Add final and assign the value in the constructor.

public class MyClass
{
    private final String myVar;

    public MyClass(DataObj dataObj)
    {
        myVar = dataObj.getFinalVarValue(); // the only assignment/init happens here.
    }

    ....
}

Upvotes: 14

David B
David B

Reputation: 2698

Make it private, and then don't include a setter. As long as you never change it in within the class methods, it's immutable.

Upvotes: 1

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