Initial Values for Variables
This section discusses what value, if any, is assigned to a variable when no explicit initial value is provided in the declaration.
Default Values for Fields
Default values for fields of primitive data types and reference types are listed in Table 3.1. The value assigned depends on the type of the field.
Table 3.1 Default Values
| Data type | Default value |
| boolean | false |
| char | ‘\u0000’ |
| Integer (byte, short, int, long) | 0L for long, 0 for others |
| Floating-point (float, double) | 0.0F or 0.0D |
| Reference types | null |
If no explicit initialization is provided for a static variable, it is initialized with the default value of its type when the class is loaded. Similarly, if no initialization is provided for an instance variable, it is initialized with the default value of its type when the class is instantiated. The fields of reference types are always initialized with the null reference value if no initialization is provided.
Example 3.1 illustrates the default initialization of fields. Note that static variables are initialized when the class is loaded the first time, and instance variables are initialized accordingly in every object created from the class Light.
Example 3.1 Default Values for Fields
public class Light {
// Static variable
static int counter; // Default value 0 when class is loaded
// Instance variables:
int noOfWatts = 100; // Explicitly set to 100
boolean indicator; // Implicitly set to default value false
String location; // Implicitly set to default value null
public static void main(String[] args) {
Light bulb = new Light();
System.out.println(“Static variable counter: ” + Light.counter);
System.out.println(“Instance variable noOfWatts: ” + bulb.noOfWatts);
System.out.println(“Instance variable indicator: ” + bulb.indicator);
System.out.println(“Instance variable location: ” + bulb.location);
}
}
Output from the program:
Click here to view code image Static variable counter: 0
Instance variable noOfWatts: 100
Instance variable indicator: false
Instance variable location: null