Objektorientierte Programmierung

Objektorientierte
Programmierung
- Entwurf einer Klasse
Rational.java
Daniel Huson
Info I, WS 2005
Analyse und Design
• Anforderung: wir wollen mit „Rationalen Zahlen“,
Q, rechnen
• Beispiele:
55/9 × 9/7
½+33/8
3/9==6/18?
• Brauchen:
– Grundrechnenarten
– Eingabe/Ausgabe
– Hilfsfunktionen
Analyse und Design
• Anforderung: Rechnen mit „Rationalen Zahlen“
• Klasse:
Rational.java
• Variablen:
numerator (Zähler)
denominator (Nenner)
• Methoden:
add, subtract, multiple, divide,
equals, clone,
parse, toString,
toFloat, sign
• Private Methoden: normalize, gcd
Datei Rational.java
public class Rational {
// Variables:
private int numerator;
private int denominator;
// Constructor:
public Rational () {
numerator=0;
denominator=1;
}
// Methods:
...
}
Datei Rational.java, Forts.
public class Rational {
// Variables:
private int numerator;
private int denominator;
// Constructor:
public Rational () {
numerator=0;
denominator=1;
}
public Rational (int p,int q) {
numerator=p;
denominator=q;
normalize();
}
}
Datei Rational.java, Forts.
public class Rational {
...
// Methods:
public Rational add (Rational r) {
int p=numerator*r.denominator+
r.numerator*denominator;
int q=denominator*r.denominator;
return new Rational(p,q);
}
}
Datei Rational.java, Forts.
public class Rational {
...
// Methods:
public Rational subtract (Rational r) {
int p=numerator*r.denominatorr.numerator*denominator;
int q=denominator*r.denominator;
return new Rational(p,q);
}
}
Datei Rational.java, Forts.
public class Rational {
...
// Methods:
public void multiple (Rational r){
int p=numerator*r.numerator;
int q=denominator*r.denominator;
return new Rational(p,q);
}
}
Datei Rational.java, Forts.
public class Rational {
...
// Methods:
public void divide (Rational r) {
int p=numerator*r.denominator;
int q=denominator*r.numerator;
return new Rational(p,q);
}
}
Datei Rational.java, Forts.
public class Rational {
...
// Methods:
public boolean equals (Rational r) {
return numerator=r.numerator
&& denominator==r.denominator;
}
public Object clone (Rational r) {
return new Rational(numerator,denominator);
}
}
Datei Rational.java, Forts.
public class Rational {
...
// I/O methods:
public Rational parse (String str)
{
StringTokenizer st=new StringTokenizer(str);
int p=Integer.parseInt(st.nextToken(“/“));
int q=Integer.parseInt(st.nextToken());
return new Rational(p,q);
}
public String toString ()
{
return numerator+“/“+denominator;
}
}
Datei Rational.java, Forts.
public class Rational {
...
// Private methods:
private void normalize (){
if(denominator==0)
{
numerator=0;
denominator=1;
}
else if(denominator<0)
{
numerator= -numerator;
denominator= -denominator;
}
int z=lcd(denominator,numerator);
numerator/=z;
denominator/=z;
}
Datei Rational.java, Forts.
public class Rational {
...
// Private methods:
private int lcd (int a, int b){
while (a != b)
if (a > b)
a = a - b;
else
b = b - a;
return a;
}
}
public static void main (String[] args) throws Exception
{
BufferedReader r=new BufferedReader(new
InputStreamReader(System.in));
while(true)
{
System.out.print("? ");
String str=r.readLine();
if(str==null)
break;
StringTokenizer st=new StringTokenizer(str);
Rational a=new Rational();
a.parse(st.nextToken(" "));
char ch=(st.nextToken(" ")).charAt(0);
Rational b=new Rational();
b.parse(st.nextToken(" "));
Rational result;
switch(ch){
case '+': result=a.add(b); break;
case '-': result=a.subtract(b); break;
case '*': result=a.multiple(b); break;
case '/': result=a.multiple(b); break;
default:
System.err.println("Unknown command: "+ch);
result=new Rational(0,1);
}
System.out.println(a+" "+ch+" "+b+" = "+result);
}
}
Programmlauf:
? 1/3 + 1/3
1/3 + 1/3 = 2/3
? 9/7 + 3/4
9/7 + 3/4 = 57/28
? 57/28 - 3/4
57/28 - 3/4 = 9/7
? 1/2 * 1/3
1/2 * 1/3 = 1/6
? 1/2 / 1/2
1/2 / 1/2 = 1/4
?