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Comp 401 Metamorphosis: Casting vs. Conversion

Comp 401 Metamorphosis: Casting vs. Conversion. Instructor: Prasun Dewan. Prerequisite. Interfaces Types Math Deep vs. Shallow Copy (Optional). Metamorphosis?. Point point = new ACartesianPoint (50, 100); point = ( APolarPoint ) point;.

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Comp 401 Metamorphosis: Casting vs. Conversion

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  1. Comp 401Metamorphosis: Casting vs. Conversion Instructor: Prasun Dewan

  2. Prerequisite • Interfaces • Types Math • Deep vs. Shallow Copy (Optional)

  3. Metamorphosis? Point point = newACartesianPoint (50, 100); point = (APolarPoint) point; Class cast exception, Java cast does not automatically convert an instance of a class to an instance of another class It does not even automatically (deep) copy Ambiguous semantics Point point = newAMutablePoint (50, 100); point = (ABoundedPoint) point; Value of additional properties (upper and lower right corner)?

  4. As Methods for Metamorphosis publicclassAConvertibleCartesianPoint extendsAMutablePointimplementsConvertiblePoint { publicAConvertibleCartesianPoint(inttheX, inttheY) { super (theX, theY); } publicConvertiblePointasCartesianPoint() { returnthis; // could also clone } publicConvertiblePointasPolarPoint() { return newAConvertiblePolarPoint(getRadius(), getAngle()); } } ConvertiblePoint point = newAConvertibleCartesianPoint (50, 100); point = point.asPolarPoint(); Programmer decides what correct conversion means

  5. Automatic Conversion of Primitive Values Java cast does not automatically convert an instance of a class to an instance of another class intintVal = 5; longlongVal = intVal; doubledoubleVal = intVal; longVal = Long.MAX_VALUE; intVal = (int) longVal; In each of the multi-type assignments, a primitive memory value copied and stored in another primitive memory value of different size In the last case, cast forces conversion

  6. PrimitiveAnother Primitive intintVal = 5; longlongVal = intVal; doubledoubleVal = intVal; longVal = Long.MAX_VALUE; intVal = (int) longVal; memory 5 -1 5 5.0 9223372036854775807

  7. Primitive  Object intVal = (int) longVal; Integer integerVal = intVal; int intVal2 = integerVal;

  8. Wrapper Types “Joe Doe”.toString() Object 5.toString() “Joe Doe”.equals(5) Extends “Joe Doe”.equals(new Integer(5)) AString History String Number 5 + new Integer(5) 5 + (new Integer(5)).intValue() Integer Double Character Boolean Wrapper classes Wraps, contains Primitive types int double char bool Java automatically converts between primitive and wrapper types when assigning an expression to a variable

  9. Manual Wrapping and Unwrapping • Integer • public Integer(int value) • publicintintValue() • Double • public Double(double value) • publicdoubledoubleValue() • Boolean • public Boolean(boolean value) • publicbooleanbooleanValue() • Character • public Character(char value) • publiccharcharValue() • Float, Short, Long

  10. Storage of Primitives and Wrapped Values inti = 5 inti 5 double d = 5.5 double d 5.5 Integer I = newInteger(i) Integer@8 5 Double D = newDouble(d) Double@16 5.5 Integer I 8 different sizes 16 Double D same size

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