Console.WriteLine("Hello world");

In Java, you would use the following code to print "Hello world" to the console:

```java
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello world");
    }
}
```

Here's a brief explanation of the code:

- `public class HelloWorld`: This is the class declaration. In Java, every application must contain a `public class` with a `main` method.
- `public static void main(String[] args)`: This is the `main` method, which is the entry point of the application. The `public` keyword means it can be accessed from outside the class, `static` means it can be called without creating an instance of the class, and `void` means it doesn't return any value.
- `System.out.println("Hello world")`: This is the statement that prints "Hello world" to the console. `System.out` is a reference to the standard output stream, and `println` is a method that prints its argument followed by a newline character.

To compile and run this code, you would save it in a file called `HelloWorld.java`, then use the following commands in the terminal:

```bash
javac HelloWorld.java
java HelloWorld
```

This will compile the code and run the `main` method, printing "Hello world" to the console.