Java List Add Unique addUniqueId(List aList, T anObj)

Description

Adds an object to the given list if identical object is missing (creates list if missing).

License

Open Source License

Declaration

public static <T> List<T> addUniqueId(List<T> aList, T anObj) 

Method Source Code

//package com.java2s;

import java.util.*;

public class Main {
    /**/*ww  w.  j  av a2s  .  co  m*/
     * Adds an object to the given list if identical object is missing (creates list if missing).
     */
    public static <T> List<T> addUniqueId(List<T> aList, T anObj) {
        return containsId(aList, anObj) ? aList : add(aList, anObj);
    }

    /**
     * Returns whether list contains identical given object (accepts null list).
     */
    public static boolean containsId(List aList, Object anObj) {
        return indexOfId(aList, anObj) >= 0;
    }

    /**
     * Adds an object to the given list and returns list (creates list if missing).
     */
    public static <T> List<T> add(List<T> aList, T anObj) {
        // If list is null, create list
        if (aList == null)
            aList = new Vector();

        // Add object
        aList.add(anObj);

        // Return list
        return aList;
    }

    /**
     * Returns index of identical given object in given list.
     */
    public static int indexOfId(List aList, Object anObj) {
        // Iterate over list objects and return index if identical exists
        for (int i = 0, iMax = size(aList); i < iMax; i++)
            if (anObj == aList.get(i))
                return i;

        // Return -1 if identical doesn't exist
        return -1;
    }

    /**
     * Returns the size of a list (accepts null list).
     */
    public static int size(List aList) {
        return aList == null ? 0 : aList.size();
    }

    /**
     * Returns the object at the given index (returns null object for null list or invalid index).
     */
    public static <T> T get(List<T> aList, int anIndex) {
        return aList == null || anIndex < 0 || anIndex >= aList.size() ? null : aList.get(anIndex);
    }
}

Related

1. addUniq(List