What is a Java String's default initial value?

Question

Consider a Java String Field named x. What will be the initial value of x when an object is created for the class x;

I know that for int variables, the default value is assigned as 0, as the instances are being created. But what becomes of String?

Answer 1

It's initialized to null if you do nothing, as are all reference types.

Answer 2

That depends. Is it just a variable (in a method)? Or a class-member?

If it's just a variable you'll get an error that no value has been set when trying to read from it without first assinging it a value.

If it's a class-member it will be initialized to null by the VM.

Answer 3

There are three types of variables:

• Instance variables: are always initialized
• Static variables: are always initialized
• Local variables: must be initialized before use

The default values for instance and static variables are the same and depends on the type:

• Object type (String, Integer, Boolean and others): initialized with null
• Primitive types:
  • byte, short, int, long: 0
  • float, double: 0.0
  • boolean: false
  • char: '\u0000'

An array is an Object. So an array instance variable that is declared but no explicitly initialized will have null value. If you declare an int[] array as instance variable it will have the null value.

Once the array is created all of its elements are assiged with the default type value. For example:

private boolean[] list; // default value is null

private Boolean[] list; // default value is null

once is initialized:

private boolean[] list = new boolean[10]; // all ten elements are assigned to false

private Boolean[] list = new Boolean[10]; // all ten elements are assigned to null (default Object/Boolean value)

Answer 4

The answer is - it depends.

Is the variable an instance variable / class variable ? See this for more details.

The list of default values can be found here.

Answer 5

Any object if it is initailised , its defeault value is null, until unless we explicitly provide a default value.