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# Type Annotations

Using Java types in TypeScript.

The important thing to note about TypeScript is that **none of our types matter**, at least as far as the runtime is concerned. Only the type checker looks at it, to help make our code more readable.

However, Java types do matter. If we're defining a new method in Java from TypeScript, we need to define the type for the method.

This is where type annotations come in. Let's take these three types: `String`, `ArrayList` and `HashMap`.

Anywhere where we need to specify a Java type, we use a type annotation.

```typescript
let typeAnnotation = String;
```

Here's an example of a type annotation. We can use the imported type itself as a type annotation if it doesn't have any generics that we're required to specify.

When we need to specify generics, we use the `.type` method.

```typescript
let typeAnnotation = ArrayList.type(String);
let otherTypeAnnotation = HashMap.type(String, ArrayList.type(String));
```

And that's it. Type Annotations are useful for when you manually convert a JS type to a specific Java type (i.e. turning an object into a HashMap), or when you're trying to extend types with new methods or constructors.