Edmen Tay

Hi All,

Firstly, I would like to thanks all of the experts in javaranch and this forum which provide me a lot of explosure in java and assistant in Mock test question. Thanks you all!! your help is much more appreciated.

I was so busy on work recently and only took this few holiday to do short mock test + practical. I did not passed the test with good score and only 68%. But I will continue to improve my java skillset. Anyone can advise what step shall I further?

Last but not least, Thanks all very much!!

Sincerely
Edmen Tay

Yes, is not "does not compile". I am sorry that I had mistaken.

The instance initializer block in the first example -- the one that tries to print "SCEA" -- will only be called if an instance of the class is created. Instance initializers run at the beginning of each constructor, immediately after any superclass constructors. In the "maClass" example, no instance of maClass is ever constructed -- i.e., there's no "new maClass()" anywhere -- so that initializer is never invoked.

I got it.

Many thanks.

Regards,
Edmen

Hi All,
I got this question from Devaka Exam Lab (Final):

public class maClass{ { System.out.println("SCEA, ");//does not compile? } static{ System.out.println("SCJP, "); } static String s1=getVal(); static String s2-"Web Component Developer, "; private static String getVal(){ System.out.print("Mobile Application Developer, "); return s2; } public static void main(String args[]){ System.out.print(s1); } }

the output is "SCJP, Mobile Application Developer, null"

But, I had tried this in IDE,

class CSuper{ { System.out.print("1"); } CSuper(){ System.out.print("2"); } } public class CDemo extends CSuper{ { System.out.print("3"); } static{ System.out.print("4"); } CDemo(){ this(4); System.out.print("5"); } CDemo(int y){ System.out.print("6"); } static void fade(){ System.out.print("7"); } public static void main(String args[]){ CDemo cd=new CDemo(); cd.fade(); CDemo.fade(); new CDemo().fade(); } }

The output is "41236577123657". The initialization block is compiled.

I just wonder why the initialization block does not compile? please help.

Many thanks,

Regards,
Edmen

Hi All, I got this question from enthuware mock test:


//in file A.java package p1; public class A { protected int i = 10; public int getI() { return i; } } //in file B.java package p2; import p1.*; public class B extends p1.A { public void process(A a) { a.i = a.i*2;//compile error } public static void main(String[] args) { A a = new B(); B b = new B(); b.process(a); System.out.println( a.getI() ); } }

variable "i" is declare as protected. how can class B cannot access "i"? please help. :roll:

regards,
Edmen

Hi,
When the program run,

Menum m1 = Menum.A;

Compiler will run constructor A(5) and then call,
Menum(int s) { this.s = s; System.out.println(s); }

and the same do for,

Menum m2 = Menum.B;
Menum m3 = Menum.C;

When calling a method floor(); compile will assign an int value to variable std. So,

variable std in m1 is 5
variable std in m2 is 30

Note, There is not method floor() in enum C(5), but floor(int y). Then compiler will look for the method in Menum which assigns 1 to variable std for m3.

This is the method of overriding and polymorphism in Java compiler.

Therefore, you will get output:
5
5
5
[5] [30] [1]

Please correct if i am wrong, Hope this help.

Edmen

String s1="ram";//creates a new object of class String, and assigns it to the reference variable s1.

String s1=new String("ram")//creates a new object of class String, and assigns it to the reference variable s1.

if,
String s1 = new String();// "" assigns to the reference variable s1
just like
String s1 = "";

Strings is final class and it is Immutable Objects. you can read more on String, StringBuilder, and StringBuffer.

Hope this help.

Regards,
Edmen

Ok, I got it. Thanks for the prompt reply.

Edmen

Hi all, this question from Enthuware SCJP5 Mock Test. I had tried the code in IDE below,

class SuperClass{ SuperClass(int i){ } } public class SubClass extends SuperClass { SubClass(int i){ super(i); } SubClass(int i, int j){//line 10, compile error } }

I hit compile error at line 10, then I explicitly declare constructor "SuperClass(){}" in SuperClass. It work fine.

Is it because of explicit declare of constructor with parameter argument in super class will need to declare constructor with no argument as well?

Can anyone help?

Many Thanks.

Edmen

Hi Punit,

Integer c = new Integer(128);
Integer d = new Integer(128);
System.out.println(c.equals(d));

It is true.

Integer MAX VALUE is 2147483647 and MIN VALUE is -2147483648

Edmen

Alright, I think i got what you trying to meant.

for array, it is not overriden and it will run,
public boolean equals(Object obj) { return this == obj; }
for wrapper class, it will be overriden and will run,
public boolean equals(Object obj) { if(obj instanceof Integer) return value == ((Integer)obj).intValue(); else return false; }

Please correct if i am wrong.

Many thanks.

Edmen.

Hi, My question from Inquisition (SCJP5 quiz by Mark Dechamps).
int[]a = new int[]{1}; int[]b = new int[]{1}; System.out.println(a.equals(b));//return false

The answer is false. Can anyone explain?

When I try,
Integer c = new Integer(1); Integer d = new Integer(1); System.out.println(c.equals(d));//return true

Many thanks,

Edmen.

Alright, I am mistaken the initialization block and constructor.

I am understand now.

Thanks Abhi.

Regards,
Edmen

Hi, my query is from SCJP5 quiz by Mark Dechamps:

class A{ synchronized{System.out.println("Chess");} //1 {System.out.println("is");} //2 void hi(){System.out.println("a cool")} //3 static{System.out.println("game");} //4 }

Answer is 1 and 3.

line 3 because of semicolon.

But, I don't understand why line 1 will not compile. Is it constructor cannot be synchronized?

Can anyone help.

Many Thanks.

Regards,
Edmen

Hi,
Below is the left out part:

lst5.add(new Object());//will not compile as it is unknown type of subclass AA


Regards,
Edmen

Hi all,
I try to understand the below code in IDE. and put some of my understanding comment
import java.util.*; public class TestGenericSuper { public static void main(String... args) { List<? super AA> lst1 = new ArrayList<AA>();//lst1 can contain AA,BB,CC,DD and unknown type that is super type of AA List<? super BB> lst2 = new ArrayList<BB>();//lst2 can contain BB,CC,DD and unknown type that is super type of BB List<? super CC> lst3 = new ArrayList<BB>();//lst3 can contain CC,DD and unknown type that is super type of CC List<? super DD> lst4 = new ArrayList<CC>();//lst4 can contain DD and unknown type that is super type of DD lst1.add(new AA()); lst1.add(new BB()); lst1.add(new CC()); lst1.add(new DD()); lst1.add(null); lst2.add(new AA());//unknown super type is BB, and "AA IS-NOT BB". Therefore, will not compile lst2.add(new BB());//will compile, unknown type is BB and "BB IS-A BB" lst2.add(new CC());//will compile, "CC IS-A BB" lst2.add(new DD());//will compile, "DD IS-A BB" lst3.add(new AA());//unknown super type is CC, and "AA IS-NOT CC". Therefore, will not compile lst3.add(new BB());//unknown super type is BB, and "BB IS-NOT CC". Therefore, will not compile lst3.add(new CC()); //will compile, "CC IS-A CC" lst3.add(new DD()); //will compile, "DD IS-A CC" lst4.add(new AA());//unknown super type is DD, and "AA IS-NOT DD". Therefore, will not compile lst4.add(new BB());//unknown super type is DD, and "BB IS-NOT DD". Therefore, will not compile lst4.add(new CC());//unknown super type is DD, and "CC IS-NOT DD". Therefore, will not compile lst4.add(new DD());//will compile, "DD IS-A DD" lst4.add(new Object());//unknown super type is DD, and "Object IS-NOT DD". Therefore, will not compile List<? extends AA> lst5 = new ArrayList<AA>();//lst5 could be contain unknown type that is subclass of AA List<? extends BB> lst6 = new ArrayList<CC>();//lst6 could be contain unknown type that is subclass of BB List<? extends CC> lst7 = new ArrayList<CC>();//lst7 could be contain unknown type that is subclass of CC List<? extends DD> lst8 = new ArrayList<DD>();//lst8 could be contain unknown type that is subclass of DD //Below all will not compiled. because lst5,6,7,8 could add any type that is subclass of their type respectively, //compiler don't know any type will be added //Therefore, A and its subclass is not unknown type for subclass of A //Except lst5.add(null); will compile because it considered as unknown type for subclass of A lst5.add(new AA()); lst5.add(new BB()); lst5.add(new CC()); lst5.add(new DD()); lst5.add(null); lst5.add(new Object()); lst6.add(new AA()); lst6.add(new BB()); lst6.add(new CC()); lst6.add(new DD()); lst7.add(new AA()); lst7.add(new BB()); lst7.add(new CC()); lst7.add(new DD()); lst8.add(new AA()); lst8.add(new BB()); lst8.add(new CC()); lst8.add(new DD()); } } class AA { } class BB extends AA { } class CC extends BB { } class DD extends CC { }

Please correct if i am wrong.

Thank you

Regards,
Edmen