Easiest way to do null checks?

I'm fairly new to this, and was told that you always need to check for nulls when they're a possibility, or things can go wrong. For me this usually happens while using hashmaps. As-is I am just using nested if statements. For example:

Code:

if(myHash.get(hashKey) != null){
    if(myHash.get(hashKey) == 0){
        //do something
    }
}

What is the easiest way to do this? Thanks

 

With HashMaps, you can do something like this:

Code:

if(myHash.containsKey(key)) {
    if(myHash.get(key) == 0) {
        System.out.println("Hey, the key's value is 0!!!111oneone");
    }
}

I use this with most things I do when working with HashMaps.

 

Ah right, forgot about containsKey(). Is there an easy way to do it with other variables and such?

 

What sort of variables are you looking at performing null checks on? They're not required in a whole lot of places.

 

Nothing other than hashmaps at this point, just wanted to be prepared in the future. Are they required before checking anything that could be null? For example, if I wanted to check the value of a Player variable but it was null, would that be a problem?

 

Basically, you can't access methods and fields of a null.

Code:java

//you CANNOT do this
null.equals("testString");
//but you can do this
"testString".equals(null);

If there is a chance that something might be null, you need to check before trying to use any of its methods and fields. Using instanceof automatically (essentially) does a null check, so this sort of thing is always safe:

Code:java

Entity ent = someUnknownMethod();
if(ent instanceof Player)
{
    //if ent is null, this will not happen
    ((Player)ent).setHealth(0);
}