CODEWITHSUNDEEP
javaobjectarraylistattributes
Anatch
Anatch

Reputation: 453

Get an Element by his attributes

What I need : Getting an Element I have created two objects from a class which has 2 attributes: id and name. After I create an object, I set it's ID and add the object to an ArrayList:

Variable variable1 = new Variable();
variable1.setID(1);
Variable variable2 = new Variable();
variable1.setID(2);
ArrayList<Variable> varList = new ArrayList<Variable>(); 
varList.add(variable1);
varList.add(variable2);

Then in my code I want to get the Element which has Id == 1 but I didn't find a method that can return me the Object by giving it the Object attribute.

Is there a method like this : Object o = getObjectByAttribute(Object.id==1) ?

Upvotes: 1

Views: 83

Answers (3)

Biju CD
Biju CD

Reputation: 5109

If you are using java8, filters(in lambda expression) is a good option.

Stream<Variable> outputList = varList.stream().filter(val -> val.getId() ==1);

outputList will contain only Variable objects with Id 1. First element can be taken from that list if it is not empty.

Ref: http://zeroturnaround.com/rebellabs/java-8-explained-applying-lambdas-to-java-collections/

Upvotes: 1

user2336315
user2336315

Reputation: 16067

Is there a method like this : Object o = getObjectByAttribute(Object.id==1) ?

No, but it's easy to create one. Create an interface Function that from an Object of type T give a property of type U.

interface Function<T, U> {
    U apply(T t);
}

Then the method:

public static <T, U> T getObjectByAttribute(List<T> objects, Function<T, U> fromAttribute, U attributeResearched) {
    for(T obj : objects) {
        if(fromAttribute.apply(obj).equals(attributeResearched)) {
            return obj;
        }
    }
    return null;
}

and how to call it:

Variable v = getObjectByAttribute(varList, new Function<Variable, Integer>() {
                       @Override
                       public Integer apply(Variable variable) {
                            return variable.id;
                       }
              }, 1);

Upvotes: 1

S. Pauk
S. Pauk

Reputation: 5318

You could make use of Collections.binarySearch() and a custom Comparator

javadoc

EDIT: code snippet:

Comparator<Variable> comparator = new Comparator<Variable>() {
    public int compare(Variable o1, Variable o2) {
        return Integer.compare(o1.getID(), o2.getID());
    }
};
Collections.sort(varList, comparator);
Variable key = new Variable();
key.setID(1);
int index = Collections.binarySearch(varList, key, comparator);

Upvotes: 1

Related Questions