Overwrite

• See also: Mirroring
• See also: Injecting

Overwrites are a powerful feature of mixins that allow to completely overwrite the code of a certain method.

Let's say we have this simple Employee class

public class Employee {

    private final String name;
    private final double salary;

    public Employee(String name, double salary) {
        this.name = name;
        this.salary = salary;
    }

    public String getName() {
        return name;
    }

    public double getSalary() {
        return salary;
    }
}

Pretty boring.. right? Well, let's say that the company needs to lower the salaries of its employees to due to high labor costs

import io.tunabytes.Mixin;
import io.tunabytes.Overwrite;
import io.tunabytes.Mirror;

@Mixin(Employee.class)
public class EmployeeMixin {

    @Mirror private double salary;

    @Overwrite
    public double getSalary() {
        return salary - 2000;
    }
}

Now, all employees will have 2000 deducted from their salaries. We can verify that:

public class EmployeeTest {

    public static void main(String[] args) {
        MixinsBootstrap.init();
        Employee employee = new Employee("David", 4000);
        System.out.println("Salary: " + employee.getSalary());
    }
}

Output:

Salary: 2000.0

Note 1: When overwriting, it is quite possible that you may need to reference to the class fields or other methods. In that case, take a look at mirroring.

Note 2: Quite often, overwriting is an overkill and we only need to do a simple addition to the method code. If this is the case, check injecting.

Note 3: Having multiple @Overwrites on the same method would simply lead to one overwrite being dismissed. Hence, it is not recommended to have more than one @Overwrite for each method, and when possible: use injection.