intro to arrays

Question 1

array

Answer 1

> Collection of values that can be treated as a unit or individually
a very useful data structure provided by Java and other programming languages
sequence of variables of the same type
objects (hence allocated on heap) with a reference on the stack

(visualize an array as a set of variables one after another)

int[] a = new int[5];

Question 2

data structure

Answer 2

mechanism for storing data in a structured way

Question 3

what does “sequence of variables of the same type” mean?

Answer 3

> Homogeneous data structure (values of the same type (“base type”) )
Size (quantity) fixed when space is allocated
Ordered

Question 4

do arrays have default values?

Answer 4

Yes!
“instance variables” of array = cells in array
are assigned default values (0 / null / etc.) when array is created

Question 5

array variable declaration

Answer 5

int[] a or int a[];

Question 6

array object creation

Answer 6

new int[5]
or combo: int[] a = new int[1];
(creates an array of 5 cells in the heap)

Question 7

array indexing

Answer 7

mechanism for accessing individual elements of an array a[0]

Question 8

to modify arrays:

Answer 8

o modify contents of cell #2 to 6 and cell #1 to 74:
a[2] = 6;
a[1] = 74;

Question 9

to use arrays

Answer 9

System.out.println(“value = “ + (a[1]-a[2]));

Question 10

why are cells are just like variables

Answer 10

They may be read: x = a[3];

They may be written: a[2] = 7;

Question 11

to process all elements in an array

Answer 11

for (int i = 0; i < a.length; i++){
…process the one element at a[i]…
}

Question 12

what does this do in heap?
int[] a = new int[5];
int[] b = a;

Answer 12

aliasing

Question 13

what does this do in heap?
int[] a = new int[5];
int[] b = new int[a.length]; 
for (int i = 0; i < a.length; i++){ 
b[i] = a[i]; 
}

Answer 13

create a new object copy

Question 14

is an array’s length mutable or immutable?

Answer 14

a.length is immutable!

Question 15

explain how to enlarge an array

Answer 15

1. Create a new larger array object
2. Copy old array contents into new object
3. Assign address of new object to variable

Question 16

how to enlarge an array int[]a

Answer 16

int[] a = new int[5]; 
int[] temp = new int[a.length + 1]; 
for (int i = 0; i < a.length; i++){ 
temp[i] = a[i]; 
} 
a = temp;

(New variabletempcreated to hold copy and previous contents of a become garbage)

Question 17

components of an array

Answer 17

Arrays= objects
Array variables= references
Array cells= variables of the base type (reference or primitive)

Question 18

how to pass arrays into methods

Answer 18

pass-by-value

Question 19

Arrays may be initialized
at declaration time
by using values enclosed in { }

(curly brackets NOT [ ])

Answer 19

Counts elements, creates array of correct size and copies elements into the array
examples:
int[] a = {5, 10, 15};
String[] b = {"John", "Mary"}; 
String[] c = {new String("Mike"), new String("Kyle")}; 
int[] d = new int[]{5, 10, 15};

Question 20

reference copy array code

Answer 20

publicstaticvoidmain(String[]args)throwsException{
Student[]array1_1=newStudent[10];
//somecodeherewhichfillsinthearraywithdata
Student[]array1_2=array1_1;
}

Question 21

shallow copy array code

Answer 21

Student[]array2_1=newStudent[10]; 
//somecodeherewhichfillsinthearraywithdata  Student[]array2_2=newStudent[array2_1.length]; 
for(intiterator=0;iterator

Question 22

deep copy array code

Answer 22

Student[]array3_1=newStudent[10];
//somecodeherewhichfillsinthearraywithdata Student[]array3_2=newStudent[array3_1.length]; for(intiterator=0;iterator