> For the complete documentation index, see [llms.txt](https://cs61b-2.gitbook.io/cs61b-textbook-2025/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://cs61b-2.gitbook.io/cs61b-textbook-2025/9.-inheritance-i-interface-and-implementation-inheritance/9.4-implementation-inheritance-default.md).

# 9.4 Implementation Inheritance, default

Previously, we had an interface List61B that only had method headers identifying **what** List61B's should do. But, now we will see that we can write methods in List61B that already have their implementation filled out. These methods identify **how** hypernyms of List61B should behave.

In order to do this, you must include the `default` keyword in the method signature.

If we define this method in List61B

```java
default public void print() {
    for (int i = 0; i < size(); i += 1) {
        System.out.print(get(i) + " ");
    }
    System.out.println();
}
```

Then everything that implements the List61B class can use the method!

However, there is one small inefficiency in this method. Can you catch it?

For an SLList, the `get` method needs to jump through the entirety of the list. during each call. It's much better to just print while jumping through!

We want SLList to print a different way than the way specified in its interface. To do this, we need to override it. In SLList, we implement this method;

```java
@Override
public void print() {
    for (Node p = sentinel.next; p != null; p = p.next) {
        System.out.print(p.item + " ");
    }
}
```

Now, whenever we call print() on an SLList, it will call this method instead of the one in List61B.