When a variable is used as a class member, java ensures that its initial value is given , preventing program runtime errors
| type of data | initial value |
|---|---|
| byte | 0 |
| short | 0 |
| int | 0 |
| long | 0L |
| char | 'u0000' |
| float | 0.0f |
| double | 0 |
| boolean | false |
| All reference types | null |
The wrapper classes of primitive data types are all reference types
| basic type |
size (bytes) |
Defaults |
Package class |
| byte |
1 |
(byte)0 |
Byte |
| short |
2 |
(short)0 |
Short |
| int |
4 |
0 |
Integer |
| long |
8 |
0L |
Long |
| float |
4 |
0.0f |
Float |
| double |
8 |
0.0d |
Double |
| boolean |
- |
false |
Boolean |
| char |
2 |
\ u0000 (null) |
Character |
If one side is a wrapper class and the other side is a basic type; or if the comparators such as <, >, <= are used, value comparison will be performed; if it finds that both sides of == are objects, it will directly compare references instead of values.