Chapter 1: Java Building Blocks Flashcards
T or F: A file can contain multiple classes.
True. But at most one public class.
T or F: A public class within the file ClassA.java can be named ClassB
False. A public class must be in a file of the same name
What is the file extension is used for bytecode files?
.class
T or F: Every java file requires a package declaration
False. Package declaration is optional
T or F: Constructors can have a return type
False
T or F: It is optional to include a constructor in a class
True. There is a default do-nothing constructor
Where do you put code initializer blocks?
Within a class, outside of methods.
Which runs first, code initializer block or field initialization?
Depends on the order they appear in the class
When does a constructor’s code block run?
After field and initializer blocks are done
T or F: You can refer to a field before it is initialized
False
What type of data does the following primitive hold?
Boolean
True or false
What type of data does the following primitive hold?
byte
8-bit integral value
What type of data does the following primitive hold?
short
16-bit integral value
What type of data does the following primitive hold?
int
32-bit integral value
What type of data does the following primitive hold?
long
64-bit integral value
What type of data does the following primitive hold?
float
32-bit floating-point value
What type of data does the following primitive hold?
double
64-bit floating-point value
What type of data does the following primitive hold?
char
16-bit Unicode value
T or F: A float literal doesn’t need the ‘f’ after it
False. Floating point literals are assumed to be doubles unless the ‘f’ is present
What is the max value of a byte?
127
What is the min value of a byte?
-128
What does it mean to have a numeric literal followed by an ‘L’?
It’s data type is long
How do you write an octal literal?
Prefix with ‘0’
How do you write a hex literal?
Prefix with ‘0x’
How do you write a binary literal?
Prefix with ‘0b’
A numeric literal can contain ‘_’. Where can’t the underscore go?
- At the beginning or end of the literal.
- Immediately before or after a decimal.
Can a primitive be null?
No, but a reference variable can be null
Can a primitive be used to call methods?
No, but reference variables can
Is
String s1, s2 = “s2;
valid?
Yes. Multiple variables of the same type can be declared on the same line. Not all need to be initialized
Is
String s1, long l1, l2 = 12L;
valid?
No. You can only declare variables in the same line if they are the same type.
What characters can identifiers start with?
Identifiers must start with a letter, $, or _. Subsequent characters can be numbers
Is ‘public’ a valid identifier?
No. ‘public’ is a reserved word in Java
Is ‘Public’ a valid identifier?
Yes. Although ‘public’ is a reserved word, Java is case sensitive, so ‘Public’ is valid
What are the two unused reserved words?
const and goto
Do local variables have default initialization?
No
What is the default value of a boolean instance variable?
false
What is the default value of a integral instance variable?
0
What is the default value of a floating point instance variable?
0.0
What is the default value of a char instance variable?
‘\u0000’ (NUL)
What is the default value of a reference instance variable?
null
What is the scope of a local variable?
The method/block in which it is defined
What is the correct order of the following elements in a file?
Import statements package declaration class declaration
Package declaration
Import statements
class declaration
- Package declaration and import statements are optional
Is System.gc() guaranteed to run?
No
What makes an object eligible for garbage collection?
It has no references pointing to it.
All references to it are out of scope
Is finalize() guaranteed to run?
No
T or F: If an object’s finalize method is called and it’s not successfully destroyed, the finalize method could run again later.
False. The finalize method can run at most one time.
What are the 6 main benefits of java?
Object oriented encapsulation platform independent robust simple secure
