Arranging values of an arrayList in a specifed order using java

Question

I was trying to find a better and optimized solution for the following scenario
I have an arrayList

ArrayList<Order> orders = new ArrayList<Order>();

and the sorted result values in orders are as follows

    {  
     medicine,    
     medicine,  
     milk,    
     milk,    
     pillow,  
     Soap,         
     toy       
}

and I have an ENUM for all these items which is

public Enum Items{  
PILLOW("pillow"),  
HARDDISK("harddisk"),  
MILK("milk"),  
SOAP("soap"),  
MEDICINE("medicine"),  
TOY("toy")    
}

My output order should be as follows

{    
milk,  
milk,  
harddisk,  
medicine,  
medicine,  
toy,  
soap,  
pillow  
}

In order to accomplish this all i was trying to do is

ArrayList<Order> resultList = new ArrayList<Order>();  
for(Order order: orders){  
if(order.getItemName.equals(Items.MILK){  
resultList.add(order);  
}    

for(Order order: orders){    
if(order.getItemName.equals(Items.MEDICINE){  
resultList.add(order);    
}  

.......  

for(Order order: orders){  
if(order.getItemName.equals(Items.PILLOW){  
resultList.add(order);  
}

If i follow the above approach, i am able to get the output order in the above specified order, but my concern is since i am looping many for loops here, I want suggestions for optimized approach.

output should be sorted in the based on the following order

1) milk 2) harddisk 3) medicine 4) toy 5) soap 6) pillow

Why would you expect that output? It's not the natural sorting. On what basis you want to perform the sorting? — Rohit Jain, Feb 16 '13 at 18:47
This answer addresses enums with custom Comparators: http://stackoverflow.com/a/519844/1598965 — Eric P., Feb 16 '13 at 18:51

score 4 · Answer 1 · answered Feb 16 '13 at 18:48

4

Instead of that you can use Collections#sort(list,comparator) where you can pass your custom comparator to get the result in certain order.

Collections.sort(list, new Comparator<Order>() {

    @Override
    public int compare(Order obj1, Order obj2) {
         // write the custom logic 
         // a negative integer, zero, or a positive integer as the first argument
         // is less than, equal to, or greater than the second
         return 0;
    }
});

answered Feb 16 '13 at 18:48

Subhrajyoti Majumder

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I appreciate the above approach but I already have orders arrayList in sorted order of ascending. All I want is to output the results in custom sorted order i.e 1) milk 2) harddisk 3) medicine 4) toy 5) soap 6) pillow – Sairaj R Feb 16 '13 at 18:57
to get custom ordering we use `Comparator`. We can write custom logic to get ordering. – Subhrajyoti Majumder Feb 16 '13 at 19:00
Also I have repeated values in the list – Sairaj R Feb 16 '13 at 19:05

JB Nizet · Answer 2 · 2013-02-16T19:05:44.653

Enums have a natural order, which is the order of the declaration of the enum members. So if you want the order you specify, the enum should be declared as:

public Enum Item {  
    MILK("milk"),  
    HARDDISK("harddisk"),  
    MEDICINE("medicine"),  
    TOY("toy"),
    SOAP("soap"),  
    PILLOW("pillow");    
}

And then you could sort your orders like this:

Collections.sort(orders, new Comparator<Order>() {
    @Override
    public int compare(Order o1, Order o2) {
        return o1.getItem().compareTo(o2.getItem());
    }
});

If you can't modify the enum, then use the following trick:

private static final List<Item> ITEMS_IN_ORDER = Arrays.asList(new Item[] {
    Item.MILK,  
    Item.HARDDISK,  
    Item.MEDICINE,  
    Item.TOY,
    Item.SOAP,  
    Item.PILLOW
});

...

Collections.sort(orders, new Comparator<Order>() {
    @Override
    public int compare(Order o1, Order o2) {
        return Integer.compare(ITEMS_IN_ORDER.indexOf(o1.getItem()),
                               ITEMS_IN_ORDER.indexOf(o2.getItem()));
    }
});

I appreciate it, but in my scenario this enum is generic i mean it is used in other modules as well, i cannot make it working for one module — Sairaj R, Feb 16 '13 at 18:59

score 0 · Answer 3 · answered Feb 16 '13 at 18:59

Well one alternative ,modify your enum class to

public Enum Items{ 
 MILK("milk",1),     
 HARDDISK("harddisk",2),
 MEDICINE("medicine",3),  
 TOY("toy",4)  
 SOAP("soap",5),  
 PILLOW("pillow",6), 

 private String name;
 private sortValue;


Items(double name, double sortValue) {
    this.name= name;
    this.sortValue= sortValue;
} 
}

use a comparator, to sort based on the sort value

Collections.sort(list,new Comparator<Fruit>() {

        public int compare(Items item1, Items item2) {
                   return item1.sortValue - item2.sortValue;

});

one advantage it has over JB Nizet is it doesnt depend on the order in which you declare values in the Enum class

good..but constraint is that i am making use of a jar file of others...i shouldn't make any changes to their existing code...All i want implement things in better from my side — Sairaj R, Feb 16 '13 at 19:04

Arranging values of an arrayList in a specifed order using java

3 Answers3