Primitives/Objects Declaration, default initialization values

问题

When declaring primitives/objects, are them initialized?

Which are the default value?

What is the behavior on class members and local fields?

What about objects declaration on class members?

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As answered below, these are the default values:

Data Type - Default Value (for fields)

byte  0
short 0
int   0
long  0L
float 0.0f
double    0.0d
char  '\u0000'
String (or any object)    null
boolean   false

Please note that objects are initialized as null

回答1:

The default value of int is 0 and that is the value it will have in both JavaSE and JavaEE unless it was assigned with another value.

You can't have an uninitialized int class member in Java (or any other primitive).

In your example you show the int is a class member, in the other example its a local variable, that is the difference.

For class members JVM will put the default values, for a local variables it makes you assign and initial value before accessing the variable.

You can check the Default Values section in Primitive Data Types for more information about the class members default values.

来源：https://stackoverflow.com/questions/13972617/primitives-objects-declaration-default-initialization-values