Java Collection Max max(Collection col)

Description

Return a Collection of all highest-valued T .

License

Apache License

Parameter

Parameter	Description
col	Collection of type T

Return

of highest-valued T or null if col is null or empty

Declaration

public static <T extends Comparable<T>> Collection<T> max(Collection<T> col) 

Method Source Code

//package com.java2s;
//License from project: Apache License 

import java.util.*;

public class Main {
    /**//  w  w w . j  ava  2s .  c o m
     * Return a {@link Collection} of all highest-valued {@code T}.
     *
     * <p>
     * For example a list containing: <pre>[1, 3, 5, 1, 1]</pre>
     * Will return: <pre>[1, 1, 1]</pre>
     *
     * @param col {@link Collection} of type {@code T}
     * @return {@link Collection} of highest-valued {@code T} or {@code null} if
     * {@code col} is {@code null} or empty
     */
    public static <T extends Comparable<T>> Collection<T> max(Collection<T> col) {
        if (col == null || col.isEmpty())
            return null;

        Collection<T> result = sizedArrayList(col.size());
        Iterator<T> it = col.iterator();
        T max = it.next();
        result.add(max);
        while (it.hasNext()) {
            T next = it.next();
            int comp = next.compareTo(max);
            if (comp > 0) {
                max = next;
                result = new ArrayList<T>();
                result.add(next);
            } else if (comp == 0) {
                result.add(next);
            }
        }
        return result;
    }

    /**
     * Return a {@link Collection} of all highest-valued {@code T}.
     *
     * <p>
     * For example a list containing: <pre>[1, 3, 5, 1, 1]</pre>
     * Will return: <pre>[1, 1, 1]</pre>
     *
     * @param col {@link Collection} of type {@code T}
     * @param c {@link Comparator} of type {@code T}
     * @return {@link Collection} of highest-valued {@code T} or {@code null}
     * if {@code col} is {@code null} or empty
     */
    public static <T> Collection<T> max(Collection<T> col, Comparator<T> c) {
        if (col == null || col.isEmpty())
            return null;

        Collection<T> result = sizedArrayList(col.size());
        Iterator<T> it = col.iterator();
        T max = it.next();
        result.add(max);
        while (it.hasNext()) {
            T next = it.next();
            int comp = c.compare(next, max);
            if (comp > 0) {
                max = next;
                result = new ArrayList<T>();
                result.add(next);
            } else if (comp == 0) {
                result.add(next);
            }
        }
        return result;
    }

    /**
     * Returns a sized array list of type {@code T}.
     *
     * @param <T> Formal type parameter
     * @param size Array list size
     * @return Array list of type {@code T}
     */
    public static <T> ArrayList<T> sizedArrayList(final int size) {
        return new ArrayList<T>(size);
    }
}

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