What is a Java String's default initial value?

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 开发者_StackOverflow社区as 0, as the instances are being created. But what becomes of String?

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

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.

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)

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.

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