java basics about String

Question

To what value is a variable of the String type automatically initialized?

Answer 1

null

Unless it's inside a method (local variable), in which case it's not declared to anything.

Answer 2

A variable of type String is a reference variable. As an instance variable, it gets initialized to null, see the specification for the discussion of other cases.

Answer 3

null

Answer 4

If the variable is a class variable, instance variable, or array component, it is initialized to null (since the default value for a reference type is null)

If the variable is a local variable, then it must be given a value explicitly (i.e. it has no default value in this case).

Answer 5

Here's a summary of the answers posted by Martin v. Löwis and silky.

We can say the following about the initialization of a String object:

• If the String is a local variable, it will not be initialized.
• If the String is a class variable, instance variable, or an array component, then it will be initialized to null.

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The reasoning is as follows:

As a variable with the type of String is a reference type, according to The Java Language Specification, Third Edition, Section 4.12.5: Initial Values of Variables says the following:

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

It goes on to say the following about the initialization of reference types:

• Each class variable, instance variable, or array component is initialized with a default value when it is created (§15.9, §15.10):
  • [removed information on irrelevant information]
  • For all reference types (§4.3), the default value is null.

And finally, the follow about local variables:

• A local variable (§14.4, §14.14) must be explicitly given a value before it is used, by either initialization (§14.4) or assignment (§15.26), in a way that can be verified by the compiler using the rules for definite assignment (§16).

Answer 6

It's null unless it's local, in which case it is technically uninitialized, but in fact you can't use it, for that reason, so the language is still type-safe. You can't deref a garbage pointer.