CODEWITHSUNDEEP
java
lisovaccaro
lisovaccaro

Reputation: 33966

Java create variable if it doesn't exist?

I'm trying to set an Array only if it doesn't exist but I cannot figure out how to do it since I get an error saying it doesn't exist:

if (null == arr) { // arr cannot be resolved to a variable
    arr = new ArrayList<task>();
}

Isn't there something such as isset() from php? Also what does <> hold?

Upvotes: 1

Views: 3477

Answers (3)

user1131435
user1131435

Reputation:

In this case, since you're initializing arr as an ArrayList type, I will assume you have already declared the type of arr as ArrayList<task> or List<Task>.

If arr has not been initialized, it will produce an error if you attempt to compare it. Thus, you must initialize arr to null:

List<task> arr = null;

This way, when you run your code, you can simply use the expression:

if(arr == null)
    arr = new ArrayList<task>();

Upvotes: 1

Ayaz Ali Khatri
Ayaz Ali Khatri

Reputation: 483

List<Task> arr=null;
if (null == arr) { // arr cannot be resolved to a variable
     arr = new ArrayList<task>();
}

it wiill work fine

Upvotes: 0

Andremoniy
Andremoniy

Reputation: 34900

No, you can not. Java is the language with strong static typing. There isn't any isset like in JS.

The only way is to declare your variable arr before and assign null value to it.

Upvotes: 1

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