Convert Kotlin MonthLoader to Java: WeekView Calendar Event Loading

Here's the converted Java code for the Kotlin MonthLoader class:

package com.alamkanak.weekview;

import java.util.Calendar;
import java.util.List;

public class MonthLoader implements WeekViewLoader {
    private MonthChangeListener onMonthChangeListener;

    public MonthLoader(MonthChangeListener onMonthChangeListener) {
        this.onMonthChangeListener = onMonthChangeListener;
    }

    @Override
    public double toWeekViewPeriodIndex(Calendar instance) {
        return instance.get(Calendar.YEAR) * 12.0 + instance.get(Calendar.MONTH) + (instance.get(Calendar.DAY_OF_MONTH) - 1) / 30.0;
    }

    @Override
    public List<? extends WeekViewEvent> onLoad(int periodIndex) {
        return onMonthChangeListener.onMonthChange(periodIndex / 12, periodIndex % 12 + 1);
    }

    public interface MonthChangeListener {
        /**
         * 
         * Very important interface, it's the base to load events in the calendar.
         * This method is called three times: once to load the previous month, once to load the next month and once to load the current month.
         * 'That's why you can have three times the same event at the same place if you mess up with the configuration'
         * 
         * @param newYear  : year of the events required by the view.
         * @param newMonth :
         * 
         *month of the events required by the view '1 based (not like JAVA API) : January = 1 and December = 12'.
         * @return a list of the events happening 'during the specified month'.
         */
        List<? extends WeekViewEvent> onMonthChange(int newYear, int newMonth);
    }
}

Explanation:

• The MonthLoader class implements the WeekViewLoader interface, responsible for loading events in the WeekView calendar.
• The MonthChangeListener interface is used to define the method onMonthChange, which is called to retrieve events for a specific month.
• onMonthChange takes the year and month as arguments (month is 1-based, starting with January as 1).
• The onLoad method of MonthLoader calls onMonthChange to fetch events based on the periodIndex (representing a specific month in the calendar).

Key Points:

• Ensure you correctly implement the MonthChangeListener interface to provide the necessary event data for the calendar.
• The onMonthChange method will be called multiple times to load events for different months, so carefully manage event data to avoid duplicates or inconsistencies.