What's the difference between calling Double.valueOf(String s) and new Double(String s)?
So I've got a String and I want to create a Double object with the String as a value.
I can call
Double myDouble = new Double (myString);
or I can call
Double myDouble = Double.valueOf(myString);
Is there a difference? I'm guessing the first guarantees a new object is created on the heap and the second might re-use an existing object.
For extra credit: the string might be null, in which case I want the Double to be null, but both the above throw a NullPointerException. Is there a way of writing
Double myDouble = myString == null ? null : Double.valueOf(myString);
in less code?
Depends on the implementation. openJDK 6 b14 uses this implementation of Double(String s)
:
this(valueOf(s).doubleValue());
So it calls valueOf(String s)
internally and must be less efficient compared to calling that method directly.
Your assumption is right. The second way of getting a Double out of String can be faster because the value may be returned from a cache.
Regarding the second question, you may create a helper null safe method which would return a null instead of throwing NullPointerException.
from apache
public static Double valueOf(String string) throws NumberFormatException {
return new Double(parseDouble(string));
}
&
public Double(String string) throws NumberFormatException {
this(parseDouble(string));
}
from sun[oracle ] jdk
public Double(String s) throws NumberFormatException {
// REMIND: this is inefficient
this(valueOf(s).doubleValue());
}
&
public static Double valueOf(double d) {
return new Double(d);
}
No difference whatsoever, at least in Oracle JDK 1.6:
public Double(String s) throws NumberFormatException {
// REMIND: this is inefficient
this(valueOf(s).doubleValue());
}
If you are concerned about performance you should consider using a primitive.
double myDouble = Double.parseDouble(myString);
this will either return a valid Double, or null otherwise.
Double myDouble = null;
try {
myDouble = Double.valueOf(myString);
}
catch (Exception e) { }
it handles even when myString is null
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