SCJP 6.0 code snippets – Part 1

Posted by ski | Filed under Developement

Since I started to study to SCJP, I’ll put here some notes. I learn reading SCJP Sun Certified Programmer for Java 6, and making some small code snippets, I’ll paste them + notes here, maybe you’ll find it usefull. I think everyone who learns to SCJP should do his/her own, but if you don’t have time, or want to come back to topic, or something else, you can tak a look on those.

Moreover, please note that

  • all uncommented code is COMPILABLE
  • parts commented usually do not compile, reason is explained in a comment.
  • “dupa” means “ass” in polish ( and it’s used a lot like “foo” and “bar” :) )
  • Each section is separate java file
  • Names are a bit strange, but it’s like this to keep orderd inside package

Ready – set – go

basics, identifiers


/**
* mgorski.pl, This code is published under Creative Commons licence.
* @author Marcin Górski , 2009.
**/

package scjp;

public class S001Identifiers {

/**
* @param args
*/
public static void main(String[] args) {
int _a;
int $c;
int ______2_w;
int _$;
int €;
int £;

/** NOT LEGAL */
//        int :b;
//        int -d;
//        int e#;
//        int .f;
//        int 7g

/**
*  most weird keywords:
*      strictfp   assert (1.4)   enum (1.5)  native  goto default
*/

}

class JavaBeanClass {
//        public void setMyValue(int v);
//        public int getMyValue();
//        public boolean isMyStatus();
//        public void addMyListener(MyListener m);
//        public void removeMyListener(MyListener m);
//
//        /** NOT VALID!!!*/
//        void setCustomerName(String s) // must be public
//        public void modifyMyValue(int v) // can't use 'modify'
//        public void addXListener(MyListener m) // listener type mismatch

}

//

//

// ,
}

package must be over import
import between package and class
default class access ==  “package” access

class access


/**
* mgorski.pl, This code is published under Creative Commons licence.
* @author Marcin Górski , 2009.
**/

package scjp;

public class S002ClassAccess {

}

// default access
class Ass {
}

class A {
};

final class B {
}

// private class C {} // wrong ( outside of the public class)
// protected class D {} // wrogn!!
strictfp final class E {
}; // IEEE 754 rules of floating point
// abstract final class E {}; // wrong!

class NotAbstract {
// abstract method dupa(); // wrong!
}

abstract class CarAbstract {
final void eatThis() {
};

private final void eatThis4() {
}; // only warning!

public final void eatThis2() {
};
}

bounce


/**
* mgorski.pl, This code is published under Creative Commons licence.
* @author Marcin Górski , 2009.
**/

package scjp;

import java.io.Serializable;

public interface S003Bounceable {

public static int MAX = 100;
// public static volatile int MAX2 = 100; // wrong! wrong!
public static final int MAX3 = 100;

void bounce();

// private void bouncePrivate(); // wrong
// protected void bouncePrivateProt(); // wrong
public void bouncePrivatePub();

abstract void dupa();
// static void eatCock(); // wrong and bad name
}

interface Two extends S003Bounceable, Serializable {

}

class Dupa implements S003Bounceable {

@Override
public void bounce() {
// MAX3 = 3; // WRONG
// MAX = 100;
}

@Override
public void bouncePrivatePub() {
// TODO Auto-generated method stub

}

@Override
public void dupa() {
// TODO Auto-generated method stub

}

}

member modifiers


/**
* mgorski.pl, This code is published under Creative Commons licence.
* @author Marcin Górski , 2009.
**/

package scjp;

public class S004MemberModifiers {

private int a = 0;
public int b = 1;

protected void dupa() {
System.out.println("DUPA = " + a + "," + b);
a++;

}

public static void main(String[] args) {
Ext e = new Ext();
e.doSth();
}
}

class Ext extends S004MemberModifiers {

public void doSth() {
dupa();

}

}

default member access


/**
* mgorski.pl, This code is published under Creative Commons licence.
* @author Marcin Górski , 2009.
**/

package scjp;

public class S005DefaultMemberAccess {

public void testPublic() {
};

protected void testProtect() {
};

private void testPriv() {
};

void testDefault() {
};
}

class Extension extends S005DefaultMemberAccess {

@Override
void testDefault() {
// TODO Auto-generated method stub
super.testDefault();
}

@Override
protected void testProtect() {
// TODO Auto-generated method stub
super.testProtect();
}

protected int testPriv() {
return 0;
} // OK!

}

# def member access – same pkg


/**
* mgorski.pl, This code is published under Creative Commons licence.
* @author Marcin Górski , 2009.
**/

package scjp;

public class S005DefaultMemberAccessSamePkg {

public static void main(String[] args) {

S005DefaultMemberAccess dm = new S005DefaultMemberAccess();
dm.testDefault();
dm.testProtect();
dm.testPublic();

System.out.println("ALL ok");
}

}

other modifiers


/**
* mgorski.pl, This code is published under Creative Commons licence.
* @author Marcin Górski , 2009.
**/

package scjp;

public strictfp class S006OOtherModifiers {

native void methodInC(); // like abstract

//    synchronized abstract void syncMe(); // not allowed with abstract!

synchronized  void syncMe(){ } ;;;; // mark no implementation

strictfp long method(){ return 1L;};

public void dupa( int dupa, String...strings ){

}
}

local variable init


/**
* mgorski.pl, This code is published under Creative Commons licence.
* @author Marcin Górski , 2009.
**/

package scjp;

public class S007LocalVariables {

int a;
// final int af; // do not allow default value for final
final int af2 = 0;

public void doMe() {
int b; // not initialized (only warning) !!!!
// af2 = 3; // cannot reassign WRONG!!

System.out.println("read a = " + a);
// System.out.println( "read a = " + b); // wrong !
}

public static void main(String[] args) {
S007LocalVariables s = new S007LocalVariables();
s.doMe();
}

}

enum with a variable assigned


/**
* mgorski.pl, This code is published under Creative Commons licence.
* @author Marcin Górski , 2009.
**/

package scjp;

public enum S009Enum {

BIG(10), SMALL(5) {
@Override
public String getCode() { // this overrides code for SMALL
return "B";
}
};

S009Enum(int size) {
this.size = size;

}

private int size;

public int getSize() {
return size;
}

public String getCode() {
return "A";
}

}

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Permalink | Comments (0) | Sep 25, 2009

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