Passing inferred variables to a method

Though the use of var is limited to the declaration of local variables, these variables (both primitive and reference) can be passed to methods as values. The inferred types and the types expected by the methods must match, to allow the code to compile.

In the following example code, the Child class implements the MarathonRunner interface. The start() method in the Marathon class expects the MarathonRunner object (the instances of the class implementing this interface) as its method argument. The inferred type of the aRunner variable is Child. Since the Child class implements MarathonRunner, aRunner can be passed to the start() method, the inferred type of aRunner (Child) and the expected type of start() (MarathonRunner) match, allowing the code to compile.

The code is as follows:

interface MarathonRunner { 
    default void run() { 
        System.out.println("I'm a marathon runner"); 
    } 
} 
class Child implements MarathonRunner { 
    void whistle() { 
        System.out.println("Child-Whistle"); 
    } 
    void stand() { 
        System.out.println("Child-stand"); 
    } 
} 
class Marathon { 
    public static void main(String[] args) { 
        var aRunner = new Child();         // Inferred type is Child 
        start(aRunner);                    // ok to pass it to method start 
                                           // (param - MarathonRunner) 
    } 
    public static void start(MarathonRunner runner) { 
        runner.run(); 
    } 
}