Java Collection Create create(Collection coll)

Description

Creates a set containing all the elements in the collection

License

Open Source License

Parameter

Parameter	Description
elements	a parameter

Declaration

public static <T> Set<T> create(Collection<T> coll) 

Method Source Code

//package com.java2s;
// Clark & Parsia, LLC parts of this source code are available under the terms of the Affero General Public License v3.

import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;

import java.util.Set;

public class Main {
    /**/*from  www.j av a  2  s  .  co  m*/
     * 
     * Creates a list containing all the elements in the array
     * 
     * @param elements
     * @return
     */
    public static <T> Set<T> create(T... elems) {
        Set<T> set = new HashSet<T>(elems.length);
        for (int i = 0; i < elems.length; i++)
            set.add(elems[i]);

        return set;
    }

    /**
     * 
     * Creates a set containing all the elements in the collection
     * 
     * @param elements
     * @return
     */
    public static <T> Set<T> create(Collection<T> coll) {
        return new HashSet<T>(coll);
    }

    /**
     * Adds the given object to the set but saves memory space
     * by allocating only the required amount for small sets. The 
     * idea is to use the specialized empty set and singleton set
     * implementations (which are immutable) for the sets of size 
     * 0 and 1. If the set is empty a new singleton set is created,
     * if set has one element we create a new set with two elements,
     * otherwise we simply add the element to the given set.This 
     * technique is most useful if the expected set size is 0 or 1. 
     *   
     * @param o 
     * @param set
     * @return
     */
    public static <T> Set<T> add(T o, Set<T> set) {
        int size = set.size();
        if (size == 0)
            set = singleton(o);
        else if (size == 1) {
            T existing = set.iterator().next();
            if (!existing.equals(o))
                set = binary(existing, o);
        } else
            set.add(o);

        return set;
    }

    public final static <T> Set<T> singleton(T o) {
        return Collections.singleton(o);
    }

    /**
     * Checks if one set is equal of another one
     * 
     * @param sub
     * @param sup
     * @return
     */
    public static <T> boolean equals(Set<T> s1, Set<T> s2) {
        return s1.size() == s2.size() && s1.containsAll(s2);
    }

    public final static <T> Set<T> binary(T o1, T o2) {
        Set<T> set = new HashSet<T>();
        set.add(o1);
        set.add(o2);

        return set;
    }
}

Related

1. createAuthorString(Collection users)
2. createCollection( final Iterable object)
3. createCollection(Collection col)
4. createCollection(Object[] objects)