CODEWITHSUNDEEP
javanullinitialization
SnakeDoc
SnakeDoc

Reputation: 14351

Uninitialized Object vs Object Initialized to NULL

I'm working in Java.

I commonly setup some objects as such:

public class Foo {
    private SomeObject someName;

    // do stuff

    public void someMethod() {
        if (this.someName != null) {
            // do some stuff
        }
    }
}

The question is: Is someName in this example equated to null, as-in I can reliably for all objects assume null-checking uninitialized objects will be accurate?

Upvotes: 110

Views: 116237

Answers (2)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726479

Correct, both static and instance members of reference type not explicitly initialized are set to null by Java. The same rule applies to array members.

From the Java Language Specification, section 4.12.5:

Initial Values of Variables

Every variable in a program must have a value before its value is used:

Each class variable, instance variable, or array component is initialized with a default value when it is created

[...] For all reference types, the default value is null.

Note that the above rule excludes local variables: they must be initialized explicitly, otherwise the program will not compile.

Upvotes: 133

Jared Nielsen
Jared Nielsen

Reputation: 3897

If an Object reference has been declared but not instantiated, its value is null.

Upvotes: 19

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