Let's start with a simple test case:
import java.lang.reflect.Field;
public class Test {
private final int primitiveInt = 42;
private final Integer wrappedInt = 42;
private final String stringValue = "42";
public int getPrimitiveInt() { return this.primitiveInt; }
public int getWrappedInt() { return this.wrappedInt; }
public String getStringValue() { return this.stringValue; }
public void changeField(String name, Object value) throws IllegalAccessException, NoSuchFieldException {
Field field = Test.class.getDeclaredField(name);
field.setAccessible(true);
field.set(this, value);
System.out.println("reflection: " + name + " = " + field.get(this));
}
public static void main(String[] args) throws IllegalAccessException, NoSuchFieldException {
Test test = new Test();
test.changeField("primitiveInt", 84);
System.out.println("direct: primitiveInt = " + test.getPrimitiveInt());
test.changeField("wrappedInt", 84);
System.out.println("direct: wrappedInt = " + test.getWrappedInt());
test.changeField("stringValue", "84");
System.out.println("direct: stringValue = " + test.getStringValue());
}
}
Anybody care to guess what will be printed as output (shown at the bottom as to not spoil the surprise immediately).
The questions are:
int
and not like Integer
?Results (java 1.5):
reflection: primitiveInt = 84
direct: primitiveInt = 42
reflection: wrappedInt = 84
direct: wrappedInt = 84
reflection: stringValue = 84
direct: stringValue = 42
Compile-time constants are inlined (at javac compile-time). See the JLS, in particular 15.28 defines a constant expression and 13.4.9 discusses binary compatibility or final fields and constants.
If you make the field non-final or assign a non-compile time constant, the value is not inlined. For instance:
private final String stringValue = null!=null?"": "42";