Merge functions for solving duplicate keys in toMap collectors

MergeUtil.java

package nl.meylingmedia.util;

import java.util.Comparator;
import java.util.function.BinaryOperator;
import java.util.function.Function;

/**
 * Merge functions for solving duplicate keys in toMap collectors.
 * 
 * @see java.util.stream.Collectors#toMap(Function, Function, BinaryOperator) 
 * @author Jan-Willem Gmelig Meyling
 */
public class MergeUtil {

    public static <T> BinaryOperator<T> usingInitialValue() {
        return (a,b) -> a;
    }

    public static <T> BinaryOperator<T> usingLastValue() {
        return (a,b) -> b;
    }

    public static <T> BinaryOperator<T> usingMaxValue(Comparator<T> comparator) {
        return (a,b) -> comparator.compare(a, b) >= 0 ? a : b;
    }

    public static <T extends Comparable<T>> BinaryOperator<T> usingMaxValue() {
        return usingMaxValue(Comparator.<T> naturalOrder());
    }

}