Lecture 5

Question 1

Java and Python difference in storing objects.

Answer 1

Java stores some values on the heap as objects.
Python stores everything.

Question 2

Java and Python difference in values not stored on the heap.

Answer 2

Java stores them at bit-sequences.
Python does not do this.

Question 3

Java and Python difference in Type information.

Answer 3

Java has type information specified in the program (at compile time).
Python stores type information in the object itself (at run time).

Question 4

Numeric types, Java vs. Python.

Answer 4

Java: Bit sequences.
Python: Objects.

Question 5

Integer range. Java vs. Python.

Answer 5

Java: Limited range.
Python: Not limited.

Question 6

Types of integers. Java vs. Python.

Answer 6

Java: Multiple types.
Python: One type.

Question 7

Types of floats. Java vs. Python.

Answer 7

Java: Multiple types.
Python: One type.

Question 8

Float ranges. Java vs. Python.

Answer 8

Java: Different types, different ranges.
Python: One type, one limited range.

Question 9

Numeric types in Java.

Answer 9

int
byte (8 bits)
short, a kind of int
long, a kind of int
double, double* precision float.
float
char, represents code units in Unicode

Question 10

Usage advice of number types for CMPT270.

Answer 10

Int for counted quantities.
Double for measured.
Others for special purposes only. Don’t worry about them too much.

Note: Java’s numeric types are very similar to C/C++.

Question 11

Java arithmetic operators.

Answer 11

Same as Python. +,-,*,/,%
int operated with int leads to int
float operated with float leads to float
mixed types operated on leads to implicit conversion to a floating point
% is restricted to integers only

Question 12

Numeric expressions. Java vs. Python.

Answer 12

Java: Results in bit sequences that can be copied somewhere.
Python: Makes a new object.

Python’s way results in extra overhead and takes a bit longer.

Question 13

Booleans in java.

Answer 13

boolean: true, false

Question 14

char in Java.

Answer 14

Literals written with single quotes. Any single letter, number, keyboard symbol.

Question 15

Strings in Java.

Answer 15

Any sequence of characters. 0 or more.
Written with double quotes.
Strings are a class*, not a primitive.

Question 16

Boolean expressions in Java.

Answer 16

&&
||
!
These are from C.

Question 17

Java rational expressions.

Answer 17

==
>=
etc…
Inherited from C.

Question 18

Where is data for primitive types stored in Java?

Answer 18

On the stack.

Question 19

How do reference types work with memory?

Answer 19

The reference type in the stack holds a pointer that leads to an object on the heap.

Question 20

Java. What happens when you set a reference type variable to another?

Answer 20

A copy of the pointer is made. Like in Python?

Question 21

Java declaring variables.

Answer 21

tell the compiler the name and type.
type name;
The compiler allocates exactly enough memory for the type.
Every variable must be declared before it can be used.

Question 22

Java. What is initializing a variable?

Answer 22

The first time a variable is assigned to something.

Question 23

How many times can a variable be declared and initialized?

Answer 23

One once for any variable. Although new values can be assigned.

Question 24

Constants in Java.

Answer 24

Use final keyword.
i.e.
final type name;

These can be useful for adding clarity to calculations.
final tells the compiler that no future changes are allowed.

Question 25

Type casting in Java.

Answer 25

Not allowed implicitly.
I.e.
double exampleDouble = 9.8;
int exampleInt = (int) exampleDouble;

exampleInt is 9
Type casting double to int truncates, not rounds.

Question 26

Scope in Java.

Answer 26

{} shows the structure.
A variable’s scope is it’s lifetime. They are not usable outside it’s scope.

Question 27

Java. Conditional statements.

Answer 27

if (condition)
{
stuff;
}
else if (condition)
{
stuff;
}
else
{
stuff;
}

Note the “else if” instead of “elif” like in python.

Question 28

Java while loops.

Answer 28

while (condition)
{
stuff;
}

Question 29

Java for loop.

Answer 29

Example:
for (int i = 0; i<10; i++)
{
stuff;
}

Question 30

Java. Do while loops.

Answer 30

do
{
stuff;
} while (condition);

Question 31

Console output in java.

Answer 31

Printing uses System.out object.
System.out.print(); has no newline
System.out.println(); has a newline.

Question 32

Java. How to get string length?

Answer 32

.length() method

Question 33

Java. String concatenation.

Answer 33

string1 + string2
This also works with other data types.