Order the elements of array list in Java

Question

I have an arraylist defined whose elements are say, [man, animal, bird, reptile]. The elements in the arraylist are non-mandatory. The list can even be empty.

I always need to give the output as [animal,man,reptile,bird]. Means, the order of the elements are to be maintained. Is there any way of doing in arraylist?

I thought I can do like

for (String listElement: customList) { //custom list variable holds all elements
    if (listElement.equalsIgnoreCase("animal"){
        newList.add(0, listElement);
} else if("man") {
    newlist.add(1, listElement);
}

But I would want to know the best practice of doing. Can someone please help me on this?

what are you trying to do? I don't see any obvious logic in your ordering example. — Blub
– Blub, Commented Dec 9, 2013 at 10:47
I want to order the elements in custom way. From [man, animal, bird, reptile] to [animal, man, reptile, bird]. The order is pre-defined. — Poppy
– Poppy, Commented Dec 9, 2013 at 10:50
@ZouZou No. Ther is no logic behind. It is just pre-defined order. — Poppy
– Poppy, Commented Dec 9, 2013 at 10:57

rewritten · Accepted Answer · 2013-12-09 10:55:44Z

2

You can define a custom sorting and use it to order your array (save the comparator somewhere, so you don't have to instantiate it many times):

List<String> definedOrder = // define your custom order
    Arrays.asList("animal", "man", "reptile", "bird");

Comparator<String> comparator = new Comparator<String>(){

    @Override
    public int compare(final String o1, final String o2){
        // let your comparator look up your car's color in the custom order
        return Integer.valueOf(definedOrder.indexOf(o1))
            .compareTo(Integer.valueOf(definedOrder.indexOf(o2)));
    }
};

Collections.sort(myList, comparator);

answered Dec 9, 2013 at 10:55

rewritten

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Comments

Infinite Recursion · Accepted Answer · 2013-12-09 11:31:15Z

1

Use a custom comparator:

    Collections.sort(customList, comparator);

    int i = 0;
    for (String temp : customList) {
        System.out.println("customList " + ++i + " : " + temp);
    }

Custom comparator below:

public static Comparator<String> comparator = new Comparator<String>() {        

    public int compare(String str1, String str2) {
        return orderOf(str1) - orderOf(str2);
    }

    private int orderOf(String name) {          
            return ((List)Arrays.asList("animal", "man", "reptile", "bird")).indexOf(name);
    }
};

answered Dec 9, 2013 at 11:31

Infinite Recursion

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Zavior · Accepted Answer · 2013-12-09 10:53:27Z

0

You can use Collections.sort(yourArrayList, new CustomComparator());

You need to create your own comparator for this, though, but it is easy.

public class CustomComparator implements Comparator<YourType>{

    @Override
    public int compare(YoyrType o1, YoyrType o2) {
        // logic for ordering the list
    }
}

answered Dec 9, 2013 at 10:53

Zavior

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Comments

Sheldon Wei · Accepted Answer · 2013-12-09 11:15:41Z

0

arraylist is ordered.
maybe you want to insert element into the list.
could you create a new list every time when you have to insert and copy each of them?

answered Dec 9, 2013 at 11:15

Sheldon Wei

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