Revised: Sep./09th/2002: Since: Dec./30th/2001
$BA0@a(B$B$G>R2p$7$?Cj>]%/%i%9$rMxMQ$9$k%5%s%W%k$r>R2p$7$^$9!#(B
$BCj>]%a%=%C%I$O!"
$BCj>]%a%=%C%I$O $BCj>]%a%=%C%I$r;}$C$?%/%i%9$OCj>]%/%i%9$K$J$j!"MxMQ$9$k$H$-$K$OCj>]%a%=%C%I$r $B8=:_$N%7%9%F%`3+H/$G$O!"@_7W$+$i $B$3$s$J$H$-$KCj>]%/%i%9$OM-0U5A$G$9!#Nc$($P!"6d9T8}:B%/%i%9$r9M$($?$H$-!"F~6b!"=P6b$N%a%=%C%I$OCj>]%/%i%9$G $B$b$&>/$78= $B%"%W%j%1!<%7%g%s$N@_7W$r$9$k$H$-!"J#?t$N%/%i%9$G9=@.$5$l$k$h$&$K$7$^$9!#%*%V%8%'%/%H;X8~$G$OJ#?t$N%*%V%8%'%/%H$,%a%C%;!<%8$r8r49$7$F=hM}$,?J$`$N$G!"0l$D0l$D$N%*%V%8%'%/%H$N5!G=$O9J$C$F$*$$$?$[$&$,3HD%@-$KIY$_!":FMxMQ$7$d$9$/$J$j$^$9!#$^$?!"A4$F$N%/%i%9$r$P$i$P$i$K $B$3$N$h$&$J@_7W$G$O!"7Q>5$5$l$k$3$H$rM=$aA[Dj$7$F!"<+J,<+?H$O%$%s%9%?%s%92=$5$l$J$$$h$&$K$7$F$*$/$3$H$,I,MW$G$9!#$^$?!"%a%=%C%I@k8@$@$1$7$F$*$$$F!" $BCj>]%a%=%C%I$O!"%a%=%C%I@k8@$@$1$G $BCj>]%/%i%9$O%$%s%9%?%s%92=$G$-$^$;$s$,!"Cj>]%/%i%97?$NJQ?t$O@k8@$G$-$^$9!#Cj>]%/%i%9$r;H$&>l9g$O!"J#?t$N%5%V%/%i%9$K7Q>5$5$l$k$3$H$rA[Dj$7$F$*$j!"$=$l$i$N7?$N%*%V%8%'%/%H!J$N;2>H(BID$B!K$rA4$FBeF~$G$-$k$N$GJXMx$G$9!#(B
$Bl9g$O!"%/%i%9(B $B$3$N$H$-!"(B $B7Q>5$NL\E*$O!"$"$k%/%i%9$G $B$7$+$7!">e$K8+$?$h$&$K!"%9!<%Q!<%/%i%97?$K7?JQ49$r
$B2sHr:v$H$7$F!"%5%V%/%i%97?$K%-%c%9%H$9$k$N$O!"$"$^$jHFMQ@-!?3HD%@-$,$"$j$^$;$s!#%-%c%9%H$9$k$K$7$F$b!"%*%V%8%'%/%H$N $B$3$l$KHf$Y$k$H!"%9!<%Q!<%/%i%9$G$b $B$=$3$G!"Cj>]%/%i%9$N%a%j%C%H$,5s$2$i$l$^$9!#(B $BL^O@!"%9!<%Q!<%/%i%9$G@k8@$7$?%a%=%C%I0J30$N$b$N$r%5%V%/%i%9$G$BCj>]%/%i%9(B
ClassB objB = objAn.getBn();
$B@_7W$H
$B%5%s%W%k(B
$BCj>]%/%i%9$r;H$o$J$$>l9g$NIT6q9g(B
Oya
$B$r7Q>5$7$F(B Ko
$B%/%i%9$rDj5A$7$F$$$^$9!#(B
class Oya {
private int price;
void setPrice(int i) {
price = i;
}
int getPrice() {
return price;
}
}
class Ko extends Oya {
int sales() {
double d = getPrice()*0.9;
return (int)d;
}
}
Ko
$B%/%i%97?$r%$%s%9%?%s%92=$7$?%*%V%8%'%/%H$r;2>H$9$kJQ?t(B koObj
$B$r(B Oya
$B7?$KJQ49$9$k$H!"(B Ko
$B%/%i%9$GDj5A$7$?%a%=%C%I(B sales()
$B$O;H$($J$/$J$j$^$9!#(BCastTest.java
:
class CastTest {
public static void main(String[] args) {
Ko koObj = new Ko();
Oya oyaObj = koObj;
oyaObj.setPrice(1980);
int i = oyaObj.sales(); // $B%3%s%Q%$%k%(%i!<(B
System.out.println(i);
}
}
C:\Java>javac CastTest.java
CastTest.java:6: $B%7%s%\%k$r2r
sales()
$B%a%=%C%I$O(B Ko
$B%/%i%9$GDj5A$5$l$F$$$k$N$G!"(B Oya
$B%/%i%97?$K7?JQ49$r
$B2r7h:v(B
$BCj>]%/%i%9$N%5%s%W%k(B
Oya.java
:
// $BCj>]%/%i%9(B
abstract class Oya {
private int price = 1980;
int getPrice() {
return price;
}
// $BCj>]%a%=%C%I(B
abstract int sales();
}
// $B
CastTest.java
:
class CastTest {
public static void main(String[] args) {
Ko1 koObj1 = new Ko1();
Oya oyaObj = koObj1;
System.out.println("Price: " + oyaObj.getPrice());
System.out.println("90%: " + oyaObj.sales());
Ko2 koObj2 = new Ko2();
oyaObj = koObj2;
System.out.println("80%: " + oyaObj.sales());
}
}
C:\Java>javac Oya.java
C:\Java>javac CastTest.jav
C:\Java>java CastTest
Price: 1980
90%: 1782
80%: 1584
C:\Java>
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