A demonstration of setting and accessing time in a unit-safe way.

ExerciseJava.java

import java.util.concurrent.TimeUnit;

public class ExerciseJava {

    private long duration;

    public void setDuration(long duration, TimeUnit unit) {
        this.duration = TimeUnit.MILLISECONDS.convert(duration, unit);
    }

    public long getDuration(TimeUnit unit) {
        return unit.convert(duration, TimeUnit.MILLISECONDS);
    }
}

Alternatively, if it makes sense. You could declare the unit and it's bindings more explicitly, but this I feel is a tradeoff for clarity.

public class ExerciseJava {

    private long duration;
    private final TimeUnit defaultUnitMillis = TimeUnit.MILLISECONDS;

    public void setDuration(long duration, TimeUnit unit) {
        this.duration = defaultUnitMillis.convert(duration, unit);
    }

    public long getDuration(TimeUnit unit) {
        return unit.convert(duration, defaultUnitMillis);
    }
}