Mo Bustany

I've seen abstract static classes being used an first level inner classes.
1. Is that the only purpose for them? What do you
buy by defining it static other than not having
an inner class per top class instance. And why is
it abstract???
2. Is there a purpose of defining a top level abstract static class?
Thank you

Page 150 of Sun Cert. by Sierra and Bates states that we get the cast from int to short for free.
short s2 = 0x7fff;
works but not this one:
short s1 = 0x8000;
public class Test { public static void main (String args[]) { short s2 = 0x8000; } }

Here is the code and the output, both print the subclass
class supcls { public static void mthd(){ System.out.println("This supercls static mthd"); } } class subcls extends supcls { public static void mthd(){ System.out.println("This subcls static mthd"); } } public class Test { public static void main(String args[]){ subcls.mthd();//calls supercls mthd subcls subob=new subcls(); subob.mthd();//ALSO CALLS MTHD IN SUPERCLS } }
This subcls static mthd This subcls static mthd

Given the following
public class EqualTest { public static void main(String[] args) { EqualTest equalTest1 = new EqualTest(); String s1 = "abc"; String s2 = "ab" + "c"; String s3 = "ab"; String s4 = s3 + "c"; if (s1 == s2) System.out.println("s1==s2"); // prints s1==s2 if (s1 == s4) System.out.println("s1==s4"); // no output!!!! if (s2.equals(s1)) System.out.println("s2 equals s1"); // prints s2 eqs s1 } }
Why isn't s1 identical to s4 but s2 is identical to s1!!!

I declared a 2-dim array of strings as final. However, I'm able to modify the contents of the array.
1. Why??
2. How can I make the contents final?
Thank you

public class Cat { public Cat() { } public void setProperties(final String[][] props) { props[1][1] = "Male"; } public void printProperties(String [][] props) { for (int i=0; i < props.length; i++) { for (int j=0; j < props[i].length; j++) System.out.print(props[i][j] + " "); System.out.println(); } } public static void main(String[] args) { Cat cat1 = new Cat(); final String[][] props = { {"Color","Brown"}, {"Gender","Female"}, {"Mood","Pleasant"}, {"Pregnant","No"} }; cat1.setProperties(props); cat1.printProperties(props); } }
[ Jess adjusted the line breaks so the page won't scroll horizontally ]
[ February 06, 2003: Message edited by: Jessica Sant ]

Barry, could you tell me what java 'rule' does my original code violates?? It looks to me it's syntactically correct.

I wholeheartedly concur. javaranch.com is a blessing and the kathy/bert book is great.

Here is the parent class (inner class).
package javacertification; /** * <p>Title: </p> * <p>Description: </p> * <p>Copyright: Copyright (c) 2003</p> * <p>Company: </p> * @author unascribed * @version 1.0 */ public class AccessControl { public abstract class Car { protected int price; public Car () { price = 10; } public Car (int p) { price = p; } public int getPrice() { return price; } } public class Volvo extends Car { public Volvo () { super(20); } public Volvo (int p) { price = p; } public int getPrice() { return price; } public int getPriceVar(Car car) { return car.price; } } public AccessControl() { } public static void main(String[] args) { AccessControl ac = new AccessControl(); AccessControl.Car v1 = ac.new Volvo(); AccessControl.Car v2 = ac.new Volvo(40); //System.out.println("Price: " + v1.getPrice()); //System.out.println("Price: " + ((AccessControl.Volvo) v1).getPriceVar(v2)); } }
And here is the subclass (in a different package.
package javacertification.pkg1; import javacertification.AccessControl; /** * <p>Title: </p> * <p>Description: </p> * <p>Copyright: Copyright (c) 2003</p> * <p>Company: </p> * @author unascribed * @version 1.0 */ public class AC_Subclass { public AC_Subclass() { } public class BMW extends AccessControl.Car { public int getPrice() {return price;} } public static void main(String[] args) { AC_Subclass AC_Subclass1 = new AC_Subclass(); } }
I get the error:
"AC_Subclass.java": Error #: 478 : enclosing class javacertification.AccessControl of class javacertification.AccessControl.Car is not in scope at line 21, column 12
What does it mean 'not in scope'!!!
[ Jess adjusted line break in the code so the page won't overflow ]
[ February 06, 2003: Message edited by: Jessica Sant ]

Yep, Francisco A Guimaraes' answer is the most valid. the Instances of A,B and C are assigned to variable of type A. So only A methods can be seen. The other m1 methods are distinctly different from the signature of m1 of A so they are never seen. PLEASE NOTE: Try this test, define a public member int variable, mVar in each of the three classes and assigned them different int values. Then use a1,a2,a3 to display them. You will get a surprising result. But first try to guess what the values will be.
<code>
public class A
{
public int mVar = 10;
......
}
public class B extends A
{
public int mVar = 20;
......
}
...........
...........
</code>

Name change done

Why does this program output AAA.
I checked the instance of a3 using instanceof and it shows 'C', so why isn't the m1() of class C getting called !!! It's driving me nuts.
---------------------
public class Inheritance
{
public class A
{
public void m1(A a)
{
System.out.println("A");
}
}

public class B extends A
{
public void m1(B b)
{
System.out.println("B");
}
}

public class C extends B
{
public void m1(C c)
{
System.out.println("C");
}
}

public static final void main (String args[])
{
Inheritance i = new Inheritance();
Inheritance.A a1 = i.new A();
Inheritance.A a2 = i.new B();
Inheritance.A a3 = i.new C();
Inheritance.C c1 = i.new C();
a1.m1(c1);
a2.m1(c1);
a3.m1(c1);
/*
System.out.println("a1: " + a1);
System.out.println("a2: " + a2);
System.out.println("a3: " + a3);
c1.m1(a1);
c1.m1(a2);
c1.m1(a3);
*/
}
}
---------------------