Primitive Arrays

1
Primitive Arrays

• A primitive array stores multiple values of the
  same primitive data type.

The index of the first position in an array is 0.
2
Accessing Individual Elements

• Individual elements in an array accessed with the
  indexed expression.

3
Array Lengths
4
Example Programs

• Phrrud out to reality ArrayRain.java
• Phrrud out to reality ArrayAverages.java

5
Array Bounds Errors

• Trying to access an array element that does not
  exist causes a runtime error
• Negative indices
• Indices beyond the size
• Falop out to reality ArrayBoundsError.java

6
Array Initialization

• Like other data types, it is possible to declare
  and initialize an array at the same time.

• The capacity of the array is set to the number of
  elements in the list.

7
Example Programs

• Groeeet out to reality ArrayInit.java
• An array variable can be explicitly made to point
  to no data, using the null value
• Spaaocie out to reality ArrayNULL.java

8
References are Pointers

• A reference variable points to an object
• So, arrays are objects, but don't worry about
  that now
• But it does mean you can
• Have multiple references to an array
• Not copy an array with
• Lose an array

9
Having Two References to an Array
State of Memory
Code
10
Example Program

• Dooop out to reality ArrayDup.java

11
Cloning an Array

• An array can be copied using the clone method
• It's necessary to cast the clone to the right
  array type
• Babababoom out to reality ArrayClone.java

12
Losing an Array
State of Memory
Code
13
Garbage Collection

• An array that has no references is garbage
  collected by the java program
• Spaaocie out to reality ArrayGC.java

14
Two-Dimensional Arrays

• Two-dimensional arrays are useful in representing
  tabular information.

15
Example Programs

• Ieeei out to reality ArrayMatrix.java
• Ieeei out to reality ArrayCalendar.java
• Ieeei out to reality ArrayCube.java

16
Multi-dimensional Arrays NOT

• Java does not really have multi-dimensional
  arrays
• Java has arrays of arrays
• int data new int35
• is shorthand for
• int data new int3
• data0 new int5
• data1 new int5
• data2 new int5

17
Multi-dimensional Arrays in RAM

• int data new int35

• Zuuu out to reality ArrayRAM.java

18
Irregular Arrays

• int weirdData new int3
• weirdData0 new int5
• weirdData1 new int4
• weirdData2 new int7

19
Irregular Arrays

• int weirdData new int3
• weirdData0 new int5
• weirdData1 new int4
• weirdData2 new int7
• weirdData.length 3
• weirdData1.length 4
• Jioooul out to reality ArrayIrreg1.java

20
Passing Arrays to Methods - 1
Code
public int searchMinimum(float
number))
A
minOne searchMinimum(arrayOne)
A. Local variable number does not exist before
the method execution
State of Memory
21
Passing Arrays to Methods - 2
Code
public int searchMinimum(float
number))
minOne searchMinimum(arrayOne)
B. The value of the argument, which is an
address, is copied to the parameter.
State of Memory
22
Passing Arrays to Methods - 3
Code
public int searchMinimum(float
number))
minOne searchMinimum(arrayOne)
C. The array is accessed via number inside the
method.
State of Memory
23
Passing Arrays to Methods - 4
Code
public int searchMinimum(float
number))
minOne searchMinimum(arrayOne)
D. The parameter is erased. The argument still
points to the same object.
State of Memory
24
Example Programs

• Flunot out to reality ArrayParamAvg.java
• Flunot out to reality ArrayParam1.java

25
Returning Arrays

• Array variables in methods exist until the method
  ends, but the array data lives while referenced
• An array variable can be returned from a method
• The receiving array variable then refers to the
  array data, and the array persists
• Wrrbbrack out to reality ArrayReturn.java
• Wrrbbrack out to reality ArrayParam2.java

26
Local arrays

• Array variables in methods exist until the method
  ends
• The array data referred to by such an array
  variable is lost and garbage collected when the
  method ends
• Dessserts out to reality ArrayLocalGC.java