How to use Builder pattern as described by Joshua Bloch's version in my ModelInput class?

Question

I am trying to use Builder Pattern for my below class.. Initially I was using constructor of my class to set all the parameters but accidentally I came across Builder pattern an

Answer 1

try this

public final class ModelInput {
    ...

    public static class Builder {
        private long userid;
        ...

        public Builder setUserId(long userId) {
            this.userId = userId;
        }
        ...

        public ModelInput build() {
            return new ModelInput(userId,...
        }
    }
}  

Answer 2

I am not familiar with the book you are referencing, but I would suggest reading the post of wikipedia regarding the Builder pattern which is rather straight forward.

An implementation could be:

public final class ModelInput {

...

    public static class Builder {
        private long userid;
        ...    

        public Builder(long userid) {
            this.userid = userid;
        }

       ...

        public ModelInput build() {
            return new ModelInput(this);
        }
    }

    private ModelInput(Builder builder){
        this.userid = builder.userid;
        this.clientid = builder.clientid;
        this.pref = builder.pref;
        this.parameterMap = builder.parameterMap;
        this.timeout = builder.timeout;
        this.debug = builder.debug;
    }

...
}

Then when you want to initialize an object, you would call

ModelInput model = new ModelInput.Builder(...).build();

Regarding the validation process, it would be essentially the same as it would be made by checking the values (either in the constructor, or in the build method).

Hope I helped!

Answer 3

Builder constructor must have the mandatory parameters. So, in your case, if userId, clientId and parameterMap are mandatory, we will have something like that:

public final class ModelInput {

    private long userid;
    private long clientid;
    private long timeout = 500L;
    private Preference pref;
    private boolean debug;
    private Map<String, String> parameterMap;

    public ModelInput(Builder builder) {
        this.userid = builder.userId;
        this.clientid = builder.clientId;
        this.pref = builder.preference;
        this.parameterMap = builder.parameterMap;
        this.timeout = builder.timeout;
        this.debug = builder.debug;
    }

    public static class Builder {
        private long userId;
        private long clientId;
        private Preference preference;
        private boolean debug;
        private Map<String, String> parameterMap;

        public Builder(long userId, long clientId, Map<String, String> parameterMap) {
            this.userId = userId;
            this.clientId = clientId;
            this.parameterMap = parameterMap;
        }

        public Builder preference(Preference preference) {
            this.preference = preference;
            return this;
        }

        public Builder debug(boolean debug) {
            this.debug = debug;
            return this;
        }

        public Builder timeout(long timeout) {
            this.timeout = timeout;
            return this;
        }

        ...

        public ModelInput build() {
            return ModelInput(this);
        }
    }

    // ModelInput getters / setters
}

And this is how to use your builder class:

String paramMap = new HashMap<String, String>();
paramMap.put("attribute", "segmentation");

ModelInput.Builder builder = new ModelInput.Builder(109739281L, 20L, paramMap);
builder.preference(Preference.SECONDARY).timeout(1000L).debug(true);

ModelInput modelInput = builder.build();

Hope this helps :)

Answer 4

To add to what the others have written:

In order to make your class immutable, you need to make parameterMap variable immutable as well. You can do that when the ModelInput class is instantiated:

private ModelInput(Builder builder){
  this.userid = builder.userid;
  this.clientid = builder.clientid;
  this.pref = builder.pref;
  this.parameterMap = Collections.unmodifiableMap(builder.parameterMap);
  this.timeout = builder.timeout;
  this.debug = builder.debug;
}

Notice the use of Collections.unmodifiablemap();

You'll also need to make your Preference instance immutable, or at least make it known that it is in fact not immutable.