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In the Complex
class discussed in Chapter
4: Tech, the two instance variables for the real and imaginary
parts are directly accessible to other classes.
In Chapter 5: Java
we discuss access modifiers like "public"
and "private".
These allow you to control access to fields and methods by other
classes and subclasses in the same or different packages.
In the ComplexImm
class, shown below, we make the instance variables private and also
we do not allow any of the methods to alter the variables after
they are set by the constructor. Instances of such a class are said
to be immutable because they are unchangeable once created.
The getReal()
and getImg()
methods allow other classes to obtain the values of the real and
imaginary parts, respectively.
Immutable classes can provide an elegant approach to the creation
of objects in some cases. For example, instances of String
are immutable. The append operations always create a new string
object. We will also see in Chapter
10: Tech that the BigInteger
and BigDecimal classes in the java.math
core language package are immutable.
The disadvantage of such an approach is that there can be some
performance tradeoffs since access to the variables must involve
method invocations and you must also create and store new objects
for every new value. In a fractal example in Chapter
11, we use the Complex
class since the intensive processing involves lots of complex number
crunching.
| ComplexImm.java |
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/**
This is a complex number class with immutable values, i.e.
* the real and img parts cannot be modified
once created. The
* "Imm" is appended to "Complex" to differentiate
this class
* from the Complex class.
*
* Most of the common complex number operations
are provided
* as static methods. New instances of ComplexImm
are created
* by the operations.
*
**/
public class ComplexImm
{
private double fReal;
private double fImg;
/** Constructor that initializes the values.
**/
ComplexImm (double r, double i) {
fReal = r; fImg = i;
} // ctor
/** Get methods for real & imaginary parts.
**/
public double getReal () {
return fReal;
} // getReal
public double getImg () {
return fImg;
} // getImg
/**
* Provide the magnitude of the complex
value.
**/
public double modulus () {
return Math.sqrt (fReal*fReal +
fImg*fImg);
} // modulus
/**
* Check for the equality of this
object with that of the argument.
**/
public boolean equals (ComplexImm cvalue) {
return ( (fReal == cvalue.getReal
()) &&
(fImg == cvalue.getImg ()) ) ;
} // equals
/**
* Define a static add method that
creates a
* a new ComplexImm object with the
sum.
**/
public static ComplexImm add (ComplexImm cvalue1,
ComplexImm cvalue2) {
double r = cvalue1.getReal () +
cvalue2.getReal ();
double i = cvalue1.getImg () +
cvalue2.getImg ();
return new ComplexImm (r,i);
} // add
/** Define a static subtract method that creates
a
* a new Complex object equal to
*
* cvalue1 - cvalue2.
**/
public static ComplexImm subtract (ComplexImm
cvalue1,
ComplexImm cvalue2) {
double r = cvalue1.getReal () -
cvalue2.getReal ();
double i = cvalue1.getImg () -
cvalue2.getImg ();
return new ComplexImm (r,i);
} // subtract
/** Define a static multiply method that creates
a
* a new ComplexImm object with the
product.
**/
public static ComplexImm multiply (ComplexImm
cvalue1,
ComplexImm cvalue2) {
double r2 = cvalue1.getReal () *
cvalue2.getReal ();
double i2 = cvalue1.getImg () *
cvalue2.getImg ();
return new ComplexImm (r2-i2, r2+i2);
} // multiply
/** Define a static divide method that creates
a
* a new ComplexImm object with the
result of
*
* cvalue1/cvalue2.
**/
public static ComplexImm divide (ComplexImm
cvalue1,
ComplexImm cvalue2) {
double denom = cvalue2.getReal ()
* cvalue2.getReal () +
cvalue2.getImg () * cvalue2.getImg ();
double r = cvalue1.getReal () *
cvalue2.getReal () +
cvalue1.getImg () * cvalue2.getImg ();
double i = cvalue1.getImg () * cvalue2.getReal
() +
cvalue1.getReal () * cvalue2.getImg ();
return new ComplexImm (r/denom,
i/denom);
} // divide
/** Return a string representation of the complex
value. **/
public String toString () {
String imgSign = (fImg < 0) ? "
- " : " + ";
return (fReal + imgSign
+ fImg + "i");
} // toString
} // ComplexImm
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References & Resources
Most recent update: June 14, 2005
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