Question

  public class Foo<T> {  
    private T value;  
    public Foo(T value){  
        this.value = value;  
    }

    public Foo<T> Is(){
        return this;
    }

    // At this point, I want a T that implements (extends) Comparable  
    // So i can compare the value.
    // How to do it in Java. 
    public  Foo<T extends Comparable> GreaterThanBar(T anotherValue)
    {
        return this;
    }

 }

This is like a builder pattern I want to do, like fluent style. Chain the methods. etc.

I have the above class, I m trying to convert from C# to Java. In C# I can add the method that where T: IComprable, it works.

How do i do this with Java? I m trying to do this on GreaterThanBar method, so that I can comparare the values.

public <T extends Comparable>  Foo<T> GreaterThan(T another)
{
    if(another.compareTo(value) > 0){
        throw new IllegalArgumentException();
    }

    return (Foo<T>) this;
}

is this the correct way of doing it? Eclipse told me to cast it but i d like to know why i need to cast it to that?

and this worked.

is there a better way to do this?

As a C# developer, I really liked how this is easy to do with C#.

Answer 1

I’m assuming you want to do something like this:

Validation<Integer> validation = new Validation<Integer>(5);
if(validation.greaterThan(3).isEqualTo(5).isOdd().isValid()) {
    //Do something for when value is valid
} else {
    //Do something for when value is invalid
}

If so, here’s a starting point:

public class Validation<T>
    private final T value;
    private boolean valid = true;

    public Validation(T value) {
        this.value = value;
    }

    public Validation<T> greaterThan(Comparable<T> another) {
        if(valid) {
            valid = another.compareTo(value) < 0;
        }        
        return this;
    }

    public boolean isValid() {
        return valid;
    }

    //Other validation methods here...
}