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Comp 401 Metamorphosis: Casting vs. Conversion

This course, led by instructor Prasun Dewan, delves into the intricacies of casting and conversion in Java. It covers essential aspects, including the differences between deep and shallow copies, and how Java manages primitive and wrapper types. You'll explore concepts like automatic conversion and the programmer's role in determining correct conversions. The material emphasizes practical applications of classes, interfaces, and the semantics of various type conversions. Prerequisites include a basic understanding of interfaces, types, and essential math.

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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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