Certified Java Programmer

Front 1

What types of characters can a legal identifier start with?

Back 1

Identifiers must start with a letter, a currency character ($), or a connecting character such as the underscore ( _ ). Identifiers cannot start with a number!

Hint 1

Identifiers cannot start with a number!

Front 2

What types of characters can a legal identifier start with?

Back 2

Alpha,
Connector (such as Underscore)
Currency ($)

Hint 2

Cannot start with numeric.

Front 3

After the first character of a identifier, what character types can be used for a legal identifier

Back 3

After the first character, identifiers can contain any combination of letters, currency characters, connecting characters, or numbers.

Front 4

What is the max. size of a name of a legal identifier?

Back 4

In practice, there is no limit to the number of characters an identifier can contain.

Front 5

What java keywords can be used as a identifier?

Back 5

None of them. You can't use a Java keyword as an identifier.

Front 6

Is the identifier named foo the same as the identifier named FOO?

Back 6

No. Identifiers in Java are case-sensitive;

Front 7

List the 50 java keywords.

Back 7

See list from book.

Front 8

What java keywords have uppercase characters in their names?

Back 8

None. All java keywords consist of lowercase letters.

Front 9

What is Sun Convention for naming a class?

Back 9

first letter should be capitalized, and if several words are linked together to form the name, the first letter of the inner words should be uppercase (a format that's sometimes called "camelCase"). For classes, the names should typically be nouns.

Front 10

What are Sun Naming Conventions for Interfaces?

Back 10

For interfaces, the names should typically be adjectives like Methods The first letter should be lowercase, and then normal camelCase

Front 11

What are Sun Conventions for Method Names?

Back 11

The first letter should be lowercase, and then normal camelCase rules should be used. In addition, the names should typically be verb-noun pairs. For example:

Hint 11

Method name should be patterned as "verb noun" format

Front 12

What are Sun standards for naming variable identifiers.

Back 12

the camelCase format should be used, starting with a lowercase letter. Sun recommends short, meaningful names, which sounds good to us.

Front 13

What are Sun conventions for naming static variables.

Back 13

Java constants are created by marking variables static and final. They should be named using uppercase letters with underscore characters as separators:

Front 14

For a Java Bean, What is the naming rule for a property that is not a boolean?

Back 14

There must be a getter method with a prefix of "get". There must be a setter method with a prefix of "set". An instance variable with the property name need not exist.

Hint 14

If the property is not a boolean, the getter method's prefix must be get. For example, getSize() is a valid JavaBeans getter name for a property named "size." Keep in mind that you do not need to have a variable named size? (although some IDEs expect it). The name of the property is inferred from the getters and setters, not through any variables in your class. What you return from getSize() is up to you.

Front 15

For a JavaBean property that is a boolean, what is the proper name of the variable?

Back 15

the property is a boolean, the getter method's prefix is either get or is. For example, getStopped() or isStopped() are both valid JavaBeans names for a boolean property.

Hint 15

Either get or is can be used as a prefix.

Front 16

For a java bean, what is a valid name for a setter method?

Back 16

The setter method's prefix must be 'set'. For example, setSize() is the valid JavaBean name for a property named size.

Front 17

What access modifier's are permitted for a setter method of a Java Bean?

Back 17

Setter method signatures must be marked public, with a void return type and an argument that represents the property type.

Front 18

For a java bean, what return types are permitted for a setter method?

Back 18

void (only)

Front 19

What are java bean rules, for a getter method?

Back 19

Getter method signatures must be marked public, take no arguments, and have a return type that matches the argument type of the setter method for that property.

Hint 19

must be public access modifier
includes no arguments
return type that matches setter method for that property.

Front 20

What are the objects called that are notified when an event occurs?

Back 20

The objects that receive the information that an event occurred are called listeners.

Front 21

Methods that add or remove listeneres from an event must conform to java bean naming standards. True or False?

Back 21

True. the methods that are used to add or remove listeners from an event must also follow JavaBean naming standards:

Front 22

What is an example of a valid listener method name that will be used to register a listener with an event source?

Back 22

Listener method names used to "register" a listener with an event source must use the prefix add, followed by the listener type. For example, addActionListener() is a valid name for a method that an event source will have to allow others to register for Action events.

Front 23

What is an example of a valid listener method name that will be used to unregister a listener from an event source?

Back 23

Listener method names used to remove ("unregister") a listener must use the prefix remove, followed by the listener type (using the same rules as the registration add method).

Front 24

What is an example of a valid argument list of a listener method used to regsiter or unregister a listener?

Back 24

The type of listener to be added or removed must be passed as the argument to the method.

Front 25

How many public class statements can be included in a valid source code file?

Back 25

There can be only one public class per source code file.

Hint 25

Test this.

Front 26

Where on a line in a source file, can comments appear?

Back 26

Comments can appear at the beginning or end of any line in the source code file; they are independent of any of the positioning rules discussed here.

Front 27

If there is a public class entered in a source file, what must the source file be named?

Back 27

If there is a public class in a file, the name of the file must match the name of the public class. For example, a class declared as public class Dog { } must be in a source code file named Dog.java.

Hint 27

Public class name should be the same as the source code file name.

Front 28

What is the positioning rule for using a package statement in a source files.

Back 28

If the class is part of a package, the package statement must be the first line in the source code file, before any import statements that may be present.

Front 29

what are the positioning rules for import statements relative to the package statement and the class declaration statement.

Back 29

If there are import statements, they must go between the package statement (if there is one) and the class declaration. If there isn't a package statement, then the import statement(s) must be the first line(s) in the source code file. If there are no package or import statements, the class declaration must be the first line in the source code file.

Front 30

If you declare multiple classes in a file, how do you organize them to use different packages or different imports.

Back 30

import and package statements apply to all classes within a source code file. In other words, there's no way to declare multiple classes in a file and have them in different packages, or use different imports.

Front 31

How many classes can be contained into one source file?

Back 31

A file can have more than one nonpublic class.

Front 32

What are the naming options for a file that does not contain any public classes?

Back 32

Files with no public classes can have a name that does not match any of the classes in the file

Front 33

What is the minimal code for a class that will compile just fine?

Back 33

class MyClass { }

Hint 33

Test

Front 34

Class Modifiers fall into two categories: access modifiers and non-access modifiers. What are the access modifiers and what do they mean?

Back 34

public - class can be accessed by any other class
protected - any class that is in the same package can be accessed
private -

Front 35

Class Modifiers fall into two categories: access modifiers and non-access modifiers. What are the non-access modifiers and what do they mean?

Back 35

strictfp, abstract, final

Front 36

There are 3 access modifiers and 4 access levels. What is the fourth access level called that is not an explicit access modifier?

Back 36

The fourth access control level (called default or package access) is what you get when you don't use any of the three access modifiers.

Front 37

All four access controls work for most method and variables declarations. But only two access controls work for class declarations. What are there names?

Back 37

Although all four access controls (which means all three modifiers) work for most method and variable declarations, a class can be declared with only public or default access; the other two access control levels don't make sense for a class, as you'll see.

Hint 37

Test

Front 38

Java is a package-centric language. What is the purpose of a package?

Back 38

Packages enable the developer to organize his classes and also clarify what version of a class to use if there is more than one class with the same class name.

Front 39

What does class Access mean? What does it mean when one Class, Class A can access Class B?

Back 39

When we say code from one class (class A) has access to another class (class B), it means class A can do one of three things:
Create an instance of class B.
Extend class B (in other words, become a subclass of class B).
Access certain methods and variables within class B, depending on the access control of those methods and variables.
In effect, access means visibility. If class A can't see class B, the access level of the methods and variables within class B won't matter; class A won't have any way to access those methods and variables.

Hint 39

Test

Front 40

What does class access mean when the class access modifier is not stated?

Back 40

Default Access A class with default access has no modifier preceding it in the declaration! It's the access control you get when you don't type a modifier in the class declaration. Think of default access as package-level access, because a class with default access can be seen only by classes within the same package. For example, if class A and class B are in different packages, and class A has default access, class B won't be able to create an instance of class A, or even declare a variable or return type of class A. In fact, class B has to pretend that class A doesn't even exist, or the compiler will complain.

Front 41

What does the public access modifier mean?

Back 41

Public Access A class declaration with the public keyword gives all classes from all packages access to the public class. In other words, all classes in the Java Universe (JU) have access to a public class.

Front 42

When do you need to use an import statement?

Back 42

if a public class you're trying to use is in a different package from the class you're writing, you'll still need to import the public class.

Front 43

When would you consider using the non-access modifier 'final'?

Back 43

You should make a final class only if you need an absolute guarantee that none of the methods in that class will ever be overridden. If you're deeply dependent on the implementations of certain methods, then using final gives you the security that nobody can change the implementation out from under you.

Front 44

What is the purpose of the non-access modifier 'abstract'?

Back 44

Abstract Classes An abstract class can never be instantiated. Its sole purpose, mission in life is to be extended (subclassed).

Hint 44

Note, however, that you can compile and execute an abstract class, as long as you don't try to make an instance of it.

Front 45

When a method is marked as abstract what changes in the body of the method?

Back 45

An abstract method does not have a body. It ends with a semi-colon.

Front 46

What non-access modifiers must be used for a class to implement an abstract method?

Back 46

If a method is in a class—as opposed to an interface—then both the method and the class must be marked abstract.

Front 47

What non-access modifier is required of a class that has a abstract method?

Back 47

if even a single method is abstract, the whole class must be declared abstract.

Front 48

When can a class be marked with the non-access modifiers 'final' and 'abstract' ?

Back 48

you can't mark a class or a method as both abstract and final. They have nearly opposite meanings. An abstract class must be subclassed, whereas a final class must not be subclassed.

Hint 48

The code will not compile.

Front 49

What is the purpose of an interface?

Back 49

When you create an interface, you're defining a contract for what a class can do, without saying anything about how the class will do it.

Front 50

What is the difference between an abstract class and an interface?

Back 50

Abstract class may have at least one abstract method. An interface has nothing but abstract methods. An interface will not have method implementations .

Front 51

What access-modifiers are allowed for an interface?

Back 51

All interface methods are implicitly declared as public and abstract.

Front 52

What variable access modifiers can be declared in an interface?

Back 52

All variables defined in an interface must be public, static, and final—in other words, interfaces can declare only constants, not instance variables.

Front 53

What non-access modifiers can be used for interface methods?

Back 53

Because interface methods are abstract, they cannot be marked final, strictfp, or native.

Front 54

What are the rules for extending an interface?

Back 54

An interface can extend another interface. An interface can extend nothing other than an interface. Interfaces don't implement anything.

Front 55

What are two ways to use non-access modifiers to declare an interface

Back 55

public abstract interface Rollable{ }
public interface Rollable{ }

Hint 55

Both of these declarations are valid and interchangeable.

Front 56

What two access modifiers can be used with an interface?

Back 56

public access and default access (package)

Front 57

What access-modifiers can be used by an Interface method?

Back 57

All interface methods are public and abstract regardless of what is in the interface definition

Hint 57

You must remember that all interface methods are public and abstract regardless of what you see in the interface definition. Look for interface methods declared with any combination of public, abstract, or no modifiers. For example, the following five method declarations, if declared within their own interfaces, are legal and identical!

Front 58

What access modifiers are considered valid declarations for interface constants?

Back 58

interface constants are defined in an interface, they don't have to be declared as public, static, or final. They must be public, static, and final, but you don't have to actually declare them that way. public, static, final is implied.

Front 59

When can the value of a constant declared in an interface be changed?

Back 59

You can't change the value of a constant! Once the value has been assigned, the value can never be modified.

Hint 59

This is due to the use of the 'final' non-access modifier.

Front 60

What are considered class members?

Back 60

instance variables and methods. local variables are not considered class members.

Front 61

What access-levels can be used for a class?

Back 61

Whereas a class can use just two of the four access control levels (default or public), members can use all four: public protected default private

Front 62

What access-levels can be used for a method?

Back 62

Whereas a class can use just two of the four access control levels (default or public), members can use all four: public protected default private

Front 63

What is the difference between the default access control and protected access control?

Back 63

Default protection is what you get when you don't type an access modifier in the member declaration. The default and protected access control types have almost identical behavior, except for one difference:

Front 64

What does it mean for code in one class to have access to a member of another class?

Back 64

For now, ignore any differences between methods and variables. If class A has access to a member of class B, it means that class B's member is visible to class A.

Front 65

What are the three ways to access a method?

Back 65

1. Put the method in the same class.
2. Invoke the method using a reference to the class the method is in.
3. Invoke an inherited method.

Front 66

What access modifiers can be used for a subclass to be able to inherit a superclass member even if both classes are not in the same package?

Back 66

For a subclass, if a member of its superclass is declared public, the subclass inherits that member regardless of whether both classes are in the same package:

Front 67

What does a reference to 'this' mean?

Back 67

The reference this always refers to the currently executing object—in other words, the object running the code where you see the this reference. Because this reference is implicit, you don't need to preface your member access code with it, but it won't hurt.

Front 68

What does the 'private' access modifier mean?

Back 68

Members marked private can't be accessed by code in any class other than the class in which the private member was declared.

Front 69

What happens when a subclass tries to access a 'private' member in it's superclass?

Back 69

When a member is declared private, a subclass can't inherit it. For the exam, you need to recognize that a subclass can't see, use, or even think about the private members of its superclass.

Front 70

Can a subclass override a superclass member that is marked private?

Back 70

No. You can, however, declare a matching method in the subclass. But regardless of how it looks, it is not an overriding method.

Front 71

What are recommended access modifiers for instance variables?

Back 71

protected or private. Getters and setters should be used to access the value of the variables. These accessor methods can then test the value to insure it is valid.

Front 72

What is the difference between default access and protected access?

Back 72

The protected and default access control levels are almost identical, but with one critical difference. A default member may be accessed only if the class accessing the member belongs to the same package, whereas a protected member can be accessed (through inheritance) by a subclass even if the subclass is in a different package.
Default and protected behavior differ only when we talk about subclasses. If the protected keyword is used to define a member, any subclass of the class declaring the member can access it through

Front 73

What access modifiers can apply to local variables?

Back 73

Access modifiers can not be applied to local variables. The only modifier that can be applied to a local variable is 'final'.

Front 74

When would you consider using 'final' on a method that is in a superclass?

Back 74

final keyword prevents a method from being overridden in a subclass, and is often used to enforce the API functionality of a method.

Front 75

What modifiers can be applied to method arguments?

Back 75

Method arguments are essentially the same as local variables. This means they can also have the modifier final. In other words, a final argument must keep the same value that the parameter had when it was passed into the method.

Front 76

Can you have an abstract class that does not contain an abstract method?

Back 76

An abstract class can be valid if it does not have any abstract methods.

Front 77

What are three clues to determine if a class is abstract or not?

Back 77

The method is not marked abstract. The method declaration includes curly braces, as opposed to ending in a semicolon. In other words, the method has a method body.
The method provides actual implementation code.

Front 78

What should you look for to find invalid concrete classes?

Back 78

Look for concrete classes that don't provide method implementations for abstract methods of the superclass.

Front 79

What is an overloaded method?

Back 79

it is simply an overloaded method (a method using the same identifier, but different arguments).

Front 80

What does the modifier synchronized mean?

Back 80

The synchronized keyword indicates that a method can be accessed by only one thread at a time.

Front 81

What access-modifiers can the synchronized modfier be combined with?

Back 81

You should also know that the synchronized modifier can be matched with any of the four access control levels (which means it can be paired with any of the three access modifier keywords).

Front 82

What class members are able to use the synchronized modifier?

Back 82

synchronized modifier can be applied only to methods—not variables, not classes, just methods.

Front 83

What is the modifer 'native' used for? What class members are able to use the 'native' modifier?

Back 83

The native modifier indicates that a method is implemented in platform-dependent code, often in C. other than Know that native is a modifier (thus a reserved keyword) and that native can be applied only to methods—not classes, not variables, just methods. Note that a native method's body must be a semicolon (;) (like abstract methods), indicating that the implementation is omitted.

Hint 83

You don't need to know how to use native methods for the exam. Native methods do not have a body.

Front 84

What is the purpose of the modifier strictfp?

Back 84

strictfp forces floating points (and any floating-point operations) to adhere to the IEEE 754 standard.

Front 85

What class members can strictfp be used with?

Back 85

Only the class and method members?

Front 86

What are Variable Argument Lists (var-args) ?

Back 86

Introduced in Java 5.0. Used to define methods that have a variable number of arguments. AKA var-args

Front 87

What are declaration rules for using var-args?

Back 87

1. Can only use one var-arg per method.
2. To declare a method using a var-arg parameter, you follow the type with an ellipsis (…), a space, and then the name of the array that will hold the parameters received.
3. The var-arg must be the last parameter in the method's signature, and you can have only one var-arg in a method.
Parameter type can be primitive or an object.

Hint 87

Example:
doStuff(Animal... animal)

Front 88

What are the differences between a constructor and a method?

Back 88

The first thing to notice is that constructors look an awful lot like methods. A key difference is that a constructor can't ever, ever, ever, have a return type…ever! Constructor declarations can however have all of the normal access modifiers, and they can take arguments (including var-args), just like methods. The other BIG RULE, to understand about constructors is that they must have the same name as the class in which they are declared. Constructors can't be marked static (they are after all associated with object instantiation), they can't be marked final or abstract

Front 89

What are the two types of variables in Java:
Once a primitive has been declared, its primitive type can never change, although in most cases its value can change.

Back 89

Primitives and Object References.

Front 90

What are the eight types of primitive variables?

Back 90

A primitive can be one of eight types: char, boolean, byte, short, int, long, double, or float.

Front 91

What is a reference variable?

Back 91

A reference variable is used to refer to (or access) an object. A reference variable is declared to be of a specific type and that type can never be changed.
A reference variable can be used to refer to any object of the declared type, or of a subtype of the declared type (a compatible type).

Front 92

For the types of integer and floating point primitives List the types in order by size of their ranges.

Back 92

Integers: byte, short, int, long.
floating point: float, double.

Front 93

What is the range of floating point types such as float and double?

Back 93

float is 32 bits long
double is 64 bits long.

Front 94

There are 6 number primitives. Name them and their size?

Back 94

byte = 1 byte
short = 2 bytes
int = 4 bytes
long = 8 bytes
a boolean does not have a range.
char 1 byte

Front 95

What is a local variable?

Back 95

Local variables are variables declared within a method.
That means the variable is not just initialized within the method, but also declared within the method.
Just as the local variable starts its life inside the method, it's also destroyed when the method has completed.
Local variables are always on the stack, not the heap.

Front 96

What modifiers can a local variable be associated with?

Back 96

variable declarations can't use most of the modifiers that can be applied to instance variables, such as public (or the other access modifiers), transient, volatile, abstract, or static, but as we saw earlier, local variables can be marked final.

Front 97

What are rules relating to initializaing local variables?

Back 97

The key is to remember that a local variable must be initialized before you try to use it. The compiler will reject any code that tries to use a local variable that hasn't been assigned a value, because—unlike instance variables—local variables don't get default values.

Front 98

What is the scoope of a local variable?

Back 98

A local variable can't be referenced in any code outside the method in which it's declared.

Front 99

Describe what an array is including the types an array can hold? Can an array hold primitives and object referencese?

Back 99

In Java, arrays are objects that store multiple variables of the same type, or variables that are all subclasses of the same type. Arrays can hold either primitives or object references,

Front 100

How do you declare an array of primitives or an array of objects?

Back 100

int [ ] myNumbers;
Customer[ ] customers;
alternate syntax is also valid:
int myNumbers[ ] ;
Customer customers [ ];

Front 101

Why would you want to use one of the Collection types in java.util instead of using an array?

Back 101

Collections can dynamically adjust their size where an array can not.

Front 102

How would you declare a 2 dimensional array?

Back 102

int [ ] [ ] myNumbers;

Front 103

How do you declare an array using a fixed size?

Back 103

You don't. You never specify the size in declaration. Size matters when the array is constructed.

Front 104

What does final mean when a primitive variable is declared as final?

Back 104

Once the variable is initialized the value will not be able to be changed for the life of the variable.

Front 105

What does final mean when a object reference variable is declared as final?

Back 105

Once the variable is initialized the object reference can not be used to refer to another object. You can modify the state of the variable but not the object that is being referenced.

Hint 105

There are no final objects, just final object references.

Front 106

What does it mean to use the transient modifier on a class member?

Back 106

Transient modifer only applies to instance variables. You mark an instance variable as transient, you're telling the JVM to skip (ignore) this variable when you attempt to serialize the object containing it.

Front 107

What does it mean to use the volatile modifier on a class member?

Back 107

The volatile modifier tells the JVM that a thread accessing the variable must always reconcile its own private copy of the variable with the master copy in memory. It only applies to instance variables.

Front 108

What are static variables?

Back 108

The static modifier is used to create variables and methods that will exist independently of any instances created for the class. All static members exist before you ever make a new instance of a class. All instances of a given class share the same value for any given static variable.

Front 109

What can you declare as static in a class?

Back 109

methods, instance variables, initialization block, nested classes.

Front 110

What is the purpose of an enum?

Back 110

In 5.0, Java lets you restrict a variable to having one of only a few pre-defined values—in other words, one value from an enumerated list. (The items in the enumerated list are called, surprisingly, enums.)

Front 111

Demonstrate how to define an enum outside of a class?

Back 111

Declaring an enum outside a class:

The however they must not be declared within a method! Declaring an enum outside a class: The preceding code can be part of a single file.

Front 112

What are enums?

Back 112

Enums are not strings or ints. They are instances of the type.