generic type binary search tree in java

Question

I want to implement a generic type binary search tree. The declarations are as follow:

public BTNode<T> {}

public class BinaryTree<T extends Comparable<T>> {}

public class BinarySearchTree <T extends Comparable<T>> extends BinaryTree<T> {}

Now I have written a class called Entry and want to store the instances of this class in the BinarySearchTree.

public class Entry implements Comparable{
private String firstName, lastName, address, phoneNumber;

public Entry(String fName, String lName, String address, String phoneNum) {
    this.firstName = fName;
    this.lastName = lName;
    this.address = address;
    this.phoneNumber = phoneNum;
}

public int compareTo(Object arg0) {
    // TODO Auto-generated method stub
    return 0;
}
}

But when I declare BinarySearchTree<Entry> bst, there is always an compile error saying:

"Bound mismatch : The type Entry is not a valid substitute for the bounded parameter > of the type BinarySearchTree"

I am still quite new to the generic type in Java. Can anybody help me solve the problem? Thanks

<T extends Comparable<T>> this line in your interface should be <T implements Comparable<T>> — Hunter McMillen
– Hunter McMillen, Commented Jun 5, 2012 at 13:47
@HunterMcMillen no it should not: extends is used in generics regardless of classes or interfaces. If you want to say T that extends Foo implements Bar, then you use <T extends Foo & Bar> — nd.
– nd., Commented Jun 5, 2012 at 13:53

Mattias Buelens · Accepted Answer · 2012-06-05 13:47:51Z

6

Your Entry class needs to implement Comparable<Entry> instead of the raw Comparable, as the raw Comparable doesn't match Comparable<T>.

public class Entry implements Comparable<Entry> { ... }

answered Jun 5, 2012 at 13:47

Mattias Buelens

20.2k4 gold badges47 silver badges52 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

nd. · Accepted Answer · 2012-06-05 13:48:12Z

5

Make your Entry class implement Comparable<Entry> so that it conforms to the contract of BinaryTree.

The contract says "all types T that extend (or implement) the type Comparable<T>". Of you replace "T" with "Entry", you see that this is required: Entry extends Comparable<Entry>

answered Jun 5, 2012 at 13:48

nd.

8,9522 gold badges34 silver badges45 bronze badges

Collectives™ on Stack Overflow

generic type binary search tree in java

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related