What is the default initialization of an array in Java?
Everything in a Java program not explicitly set to something by the programmer, is initialized to a zero value.
- For references (anything that holds an object) that is
null. - For int/short/byte/long that is a
0. - For float/double that is a
0.0 - For booleans that is a
false. - For char that is the null character
'\u0000'(whose decimal equivalent is 0).
When you create an array of something, all entries are also zeroed. So your array contains five zeros right after it is created by new.
Note (based on comments): The Java Virtual Machine is not required to zero out the underlying memory when allocating local variables (this allows efficient stack operations if needed) so to avoid random values the Java Language Specification requires local variables to be initialized.
From the Java Language Specification:
Each class variable, instance variable, or array component is initialized with a default value when it is created (§15.9, §15.10):
- For type byte, the default value is zero, that is, the value of
(byte)0.- For type short, the default value is zero, that is, the value of
(short)0.- For type int, the default value is zero, that is,
0.- For type long, the default value is zero, that is,
0L.- For type float, the default value is positive zero, that is,
0.0f.- For type double, the default value is positive zero, that is,
0.0d.- For type char, the default value is the null character, that is,
'\u0000'.- For type boolean, the default value is
false.- For all reference types (§4.3), the default value is
null.