Possible NullPointerException on Java Unboxing
2013-09-02 00:00
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What is unboxing?
Transfer a boxed object to primary types:
Boolean->boolean, Integer->int, Double->double.
Example :
Double min = decimalMetadata.getMinValue();
…
String minString = Double.toString( min );
API: public static String toString(double d)
Why a Double object can be used as parameter which require a double value?
When unboxing happened?
unboxing is done automatically by compiler in background…
Actually the code is same as below,
Double min = decimalMetadata.getMinValue();
…
String minString = Double.toString( min.doubleValue() ); //NPE problem may happen here.
See bytecode in *.class file:
2 aload_1 [min]
3 invokevirtual java.lang.Double.doubleValue() : double [165]
6 invokestatic java.lang.Double.toString(double) : java.lang.String [171]
Transfer a boxed object to primary types:
Boolean->boolean, Integer->int, Double->double.
Example :
Double min = decimalMetadata.getMinValue();
…
String minString = Double.toString( min );
API: public static String toString(double d)
Why a Double object can be used as parameter which require a double value?
When unboxing happened?
unboxing is done automatically by compiler in background…
Actually the code is same as below,
Double min = decimalMetadata.getMinValue();
…
String minString = Double.toString( min.doubleValue() ); //NPE problem may happen here.
See bytecode in *.class file:
2 aload_1 [min]
3 invokevirtual java.lang.Double.doubleValue() : double [165]
6 invokestatic java.lang.Double.toString(double) : java.lang.String [171]
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