Download array_2d

Java Programming :Array
Seree Chinodom
1
Objects for Organizing
Data
 Arrays
 The Vector Class
 Strings Revisited
2
The CS Data Challenge
 Manipulate Data
 Add
 Delete
 Replace
 Modify
 Search
 Sort
 Etc...
 Organize Data
 Class
 Subclass
 Array
 Linked List
 Tree
 Binary Tree
 Etc...
3
Scores
Write a Java program that analyzes
10 test scores.
The program should...
– …compute the sum of all of the test
scores,
– ...compute the average score, and
– ...determine whether the test was
too easy.
4
// Scores01 - average 10 exam scores with ten variables
public class Scores {
public static void main (String[] args) {
int count = 10;
int score_0 = 0;
int score_1 = 0;
int score_2 = 0;
int score_3 = 0;
int score_4 = 0;
int score_5 = 0;
int score_6 = 0;
int score_7 = 0;
int score_8 = 0;
int score_9 = 0;
int sum = 0;
int average = 0;
5
score_0 = 98;
score_1 = 82;
score_2 = 94;
score_3 = 87;
score_4 = 63;
score_5 = 99;
score_6 = 85;
score_7 = 93;
score_8 = 90;
score_9 = 75;
sum = score_0 + score_1 + score_2 +score_3 + score_4 + score_5
+ score_6 +score_7 +score_8 +score_9;
6
average = Math.round((float) sum / count);
System.out.println("sum " + sum);
System.out.println("average " + average);
if (average > 60)
System.out.println("Too easy!");
} // main
} // Scores
sum 866
average 87
Too easy!
7
Observations
 Above Task Very Common
–
–
–
–
–
–
–
driver_0
driver_1
driver_2
driver_3
car_0
car_1
car_2
Key use of computers...
Operate quickly on many, many things
 Above Technique...
Not general
Does not scale
 Need New…
– Data organizing mechanism
– Data structure
8
Array
 Ordered List of “Elements”
– Primitive data
– Objects
 Elements…
– Numbered (“indexed”) starting with 0
– Referenced via index
 Length = Number of Elements
 AKA
– List
– Vector
9
Array Illustrated
Score
Element
98
82
Index
[0]
[1]
94
87
Length=10
63
99
85
93
90
75
[9]
10
Java Arrays
We must learn how to…
 declare,
 instantiate, and
 reference
…Java arrays.
11
Declaring Arrays
 type[] variable;
– Declares variable…
–
–
–
–
• …to be a pointer to an array
• … whose elements are of type type.
Reserves memory for one pointer
Does not specify length of array
Does not reserve memory for array itself
Default value of variable is null
Arrays
are
objects!
 Examples
int[] score; // allocates pointer to array of ints
float[] gpa; // allocates pointer to array of floats
char[] name; // allocates pointer to array of chars
12
Declaring Arrays Illustrated
Address
Value
1024
1028 Null
Int[] score;
Identifier
score
1032
1036
1040
1044
1048
1052
1056
1060
1064
1068
1072
1076
1080
1084
1088
1092
13
Instantiating Arrays
 new type[ expression]
Allocates an array of…
– Type type
– Length expression
– .length == expression
 Examples
– score = new int[10]; // allocates array of 10 ints
// score.length == 10
– gpa = new float[420]; // allocates array of 420 floats
– name = new char[128] // allocates array of 128 chars
 [] vs. ()
– [] Used for arrays
– () Used for methods including constructors
14
Instantiating Arrays Illustrated
Address
Value
1024
score = new int[10];
1028
1048
Identifier
score
1032
1036
1040
1044
1048
0
1052
0
1056
0
1060
0
1064
0
1068
0
1072
0
1076
0
1080
0
1084
0
1088
1092
[0]
[1]
[9]
15
Referencing Arrays
 variable[ expression]
– [] is an operator
– References expression th element
– expression ranges from 0 to length - 1
 Examples
– score[0] = 98;
score[9] = 75;
– gpa[390] = 4.0;
– name[0] = 'D';
name[1] = 'y';
name[2] = 'k';
name[3] = 's';
name[4] = 'e';
name[5] = 'n';
Read...
“score of 0” or “score sub 0”
“gpa of 390” or “gpa sub 390”
“name of 4” or “name sub 4”
16
Referencing Arrays Illustrated
Address
Value
1024
score[0] = 98;
score[9] = 75;
1028
1048
Identifier
score
1032
1036
1040
1044
1048
98
1052
0
1056
0
1060
0
1064
0
1068
0
1072
0
1076
0
1080
0
1084
75
1088
1092
[0]
[1]
[9]
17
Array Referencing Caveat
 Once Instantiated, Array Sizes Are Fixed
 Index Must Be…
– >= 0
– <= .length - 1
 Bounds Checking
– Automatic by JVM
– Checks array index, 0 < = index <= .length - 1
– Throws exception: “Array Reference Out of Bounds”
18
Off-By-One Problems
int[] score = new int[10];
for (int i = 1; i < score.length; i++) // Error?
score[i] = 100;
for (int i = 0; i <= score.length; i++) // Error?
score[i] = 100;
for (int i = 0; i++ < score.length;) // Error?
score[i] = 100;
for (int i = 0; ++i < score.length;) // Error?
score[i] = 100;
for (int i = 0; i < score.length;) // Error?
score[++i] = 100;
for (int i = 0; i < score.length;) // Error?
score[i++] = 100;
19
Scores
Write a Java program that analyzes 10 test scores.
The program should...
 …compute the sum of all of the test scores,
 ...compute the average score, and
 ...determine whether the test was too easy.
20
// Scores02 - average 10 exam scores with one array
public class Scores {
public static void main (String[] args) {
int count = 10;
int[] score = null;
int sum = 0;
int average = 0;
score = new int[count];
score[0] = 98;
score[9] = 75;
score[1] = 82;
score[2] = 94;
score[3] = 87;
score[4] = 63;
score[5] = 99;
score[6] = 85;
score[7] = 93;
score[8] = 90;
21
sum = 0;
for (int i = 0; i < score.length; i++)
sum += score[i];
average = Math.round((float) sum / score.length);
System.out.println("sum " + sum);
System.out.println("average " + average);
if (average > 60)
System.out.println("Too easy!");
} // main
} // Scores
sum 866
average 87
Too easy!
22
Declare score
Address
int count = 10;
int[] score = null;
int sum = 0;
int average = 0;
Value
1024
10
1028
Null
1032
0
1036
0
Identifier
count
score
sum
average
1040
1044
1048
1052
1056
1060
1064
1068
1072
1076
1080
1084
1088
1092
23
Instantiating score
Address
score = new int[count];
Value
1024
10
1028
1048
1032
0
1036
0
Identifier
count
score
sum
average
1040
1044
1048
0
1052
0
1056
0
1060
0
1064
0
1068
0
1072
0
1076
0
1080
0
1084
0
1088
1092
[0]
[1]
[9]
24
Assigning Values to score
Address
score[0] = 98;
score[9] = 75;
Value
1024
10
1028
1048
1032
0
1036
0
Identifier
count
score
sum
average
1040
1044
1048
98
1052
0
1056
0
1060
0
1064
0
1068
0
1072
0
1076
0
1080
0
1084
75
1088
1092
[0]
[1]
[9]
25
Assigning More Values to score
Address
score[1] = 82;
score[2] = 94;
score[3] = 87;
score[4] = 63;
score[5] = 99;
score[6] = 85;
score[7] = 93;
score[8] = 90;
Value
1024
10
1028
1048
1032
0
1036
0
Identifier
count
score
sum
average
1040
1044
1048
98
1052
82
1056
94
1060
87
1064
63
1068
99
1072
85
1076
93
1080
90
1084
75
1088
1092
[0]
[1]
[9]
26
Average the score
sum = 0;
for (int i = 0; i < score.length; i++)
sum += score[i];
average =
Math.round((float) sum / score.length);
System.out.println("sum " + sum);
System.out.println("average " + average);
if (average > 60)
System.out.println("Too easy!");
sum 866
average 87
Too easy!
Address
Value
1024
10
1028
1048
1032
866
1036
87
Identifier
count
score
sum
average
1040
1044
1048
98
1052
82
1056
94
1060
87
1064
63
1068
99
1072
85
1076
93
1080
90
1084
75
[0]
[1]
[9]
1088
1092
27
Array Initializer List
 Used to Instantiate and Initialize an Array
 { value_1, value_2,…, value_n}
– new not used
– Length not specified (implicit)
– Allowed only with declaration
 Examples
– int[] score = {98, 82, 94, 87, 63, 99, 85, 93, 90, 75};
– char[] name = {'D', 'y', 'k', 's', 'e', 'n'};
– char[] digits = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};
28
// Scores03 - average 10 exam scores with an initializer list
public class Scores {
public static void main (String[] args) {
int[] score = {98, 82, 94, 87, 63, 99, 85, 93, 90, 75};
int sum = 0;
int average = 0;
sum = 0;
for (int i = 0; i < score.length; i++)
sum += score[i];
average = Math.round((float) sum / score.length);
System.out.println("length " + score.length);
System.out.println("sum " + sum);
System.out.println("average " + average);
if (average > 60)
System.out.println("Too easy!");
length 10
} // main
sum 866
} // Scores
average 87
Too easy!
29
Array of Objects
 Array Declaration
– Allocates a single pointer to an array of pointers
– Rectangle[] rectangle;
 Array Instantiation
– Allocates an array of pointers to objects
– rectangle = new Rectangle[4];
 Array Element Instantiation
– Allocates one object pointed to by one array element
– rectangle[0] = new Rectangle();
30
Echo.java
// Echo - echoes the command line arguments
public class Echo {
public static void main (String[] args) {
for (int i = 0; i < args.length; i++)
System.out.println("args[" + i + "] = " + args[i]);
} // main
C:\>java Echo CS 180 Rocks !
} // Echo
args[0] = CS
args[1] = 180
args[2] = Rocks
args[3] = !
31
Rectangles Class
 Data
 Methods
– width
– height
 Constructors
height
width
– Rectangle(int, int)
– Rectangle(int)
– Rectangle()
–
–
–
–
–
–
–
void setWidth(int)
int getWidth()
void setHeight(int)
int getHeight()
int area()
String toString()
boolean equals()
32
// Rectangles14 - array of rectangles
public class Main {
public static void main(String[] args) {
int total_area = 0;
Rectangle[] rectangle = null;
rectangle = new Rectangle[4];
rectangle[0] = new Rectangle();
System.out.println(
rectangle[0]
+"\n" +
rectangle[0].getWidth() + "\n" +
rectangle[0].getHeight()+ "\n" +
rectangle[0].area()
);
3 X4
3
4
12
5 X7
5
7
35
3 X4
5 X7
8 X 10
12 X 12
271
33
rectangle[1] = new Rectangle(5, 7);
System.out.println(
rectangle[1] + "\n" +
rectangle[1].getWidth() + "\n" +
rectangle[1].getHeight() + "\n" +
rectangle[1].area()
);
rectangle[2] = new Rectangle(8, 10);
rectangle[3] = new Rectangle(12);
for (int i = 0; i < rectangle.length; i++)
System.out.println(rectangle[i]);
total_area = 0;
for (int i = 0; i < rectangle.length; i++)
total_area += rectangle[i].area();
System.out.println(total_area);
} // main
} // Main
3 X4
3
4
12
5 X7
5
7
35
3 X4
5 X7
8 X 10
12 X 12
271
34
Declaring rectangle
Address
int total_area = 0;
Rectangle[] rectangle = null;
Value
Identifier
1024
0
1028
null
total_area
rectangle
1032
1036
1040
1044
1048
1052
1056
1060
1064
1068
1072
1076
1080
1084
1088
1092
35
Instantiating rectangle
Address
rectangle = new Rectangle[4];
Value
Identifier
1024
0
1028
1036
1032
1036
null
1040
null
1044
null
1048
null
total_area
rectangle
[0]
[1]
[2]
[3]
1052
1056
1060
1064
1068
1072
1076
1080
1084
1088
1092
36
Instantiating rectangle[0]
Address
Rectangle[0] = new Rectangle();
System.out.println(
rectangle[0] +
"\n" +
rectangle[0].getWidth() +
"\n" +
rectangle[0].getHeight() +
"\n" +
rectangle[0].area()
3 X4
3
);
4
12
Value
Identifier
1024
0
1028
1036
1032
1036
1060
1040
null
1044
null
1048
null
total_area
rectangle
[0]
[1]
[2]
[3]
1052
1056
1060
3
1064
4
width
height
1068
1072
1076
1080
1084
1088
1092
37
Instantiating rectangle[1]
Address
Rectangle[1] = new Rectangle(5,7);
System.out.println(
rectangle[1] +
"\n" +
rectangle[1].getWidth() +
"\n" +
rectangle[1].getHeight() +
"\n" +
rectangle[1].area()
5 X7
5
);
7
35
Value
Identifier
1024
0
1028
null
1032
1036
1060
1040
1072
1044
null
1048
null
total_area
rectangle
[0]
[1]
[2]
[3]
1052
1056
1060
3
1064
4
1068
1072
5
1076
7
width
height
width
height
1080
1084
1088
1092
38
Instantiating rectangle[2], rectangle[3]
Address
Rectangle[2] = new Rectangle(8, 10);
Rectangle[3] = new Rectangle(12);
Value
Identifier
1024
0
1028
1036
1032
1036
1060
1040
1072
1044
1080
1048
1088
total_area
rectangle
[0]
[1]
[2]
[3]
1052
1056
1060
3
1064
4
1068
1072
5
1076
7
1080
8
1084
10
1088
12
1092
12
width
height
width
height
width
height
width
height
39
Using rectangle
Address
for (int i = 0; i < rectangle.length; i++)
System.out.println(rectangle[i]);
total_area = 0;
for (int i = 0; i < rectangle.length; i++)
total_area += rectangle[i].area();
System.out.println(total_area);
Value
Identifier
1024
271
1028
1036
1032
1036
1060
1040
1072
1044
1080
1048
1088
[0]
[1]
[2]
[3]
1052
1056
1060
3
1064
4
1068
3 x4
5 x7
8 x 10
12 x 12
271
total_area
rectangle
1072
5
1076
7
1080
8
1084
10
1088
12
1092
12
width
height
width
height
width
height
width
height
40
“Multidimensional” Arrays
An Array of…
 ... arrays of...
There really are no
 …arrays of arrays of…
“multidimensional”
 …arrays of arrays of arrays of… arrays in Java.
 …arrays of arrays of arrays of…etc…of arrays of...
...Primitive Data or Objects
41
Declaring Multidimensional Arrays
 type[][]…[] variable;
Use n []’s for n
dimensional array
 Examples
– int[] array_1d; // array of ints
– int[][] array_2d; // array of arrays of ints
– int[][][] array_3d; // array of arrays of arrays of ints
42
Instantiating Multidimensional Arrays
 new type[ value_1][ value_2]…[ value_n]
Use n []’s for n dimensional array
 Examples
– array_1d = new int[3];
– array_2d = new int[3][4];
– array_3d = new int[3][4][5];
43
Referencing Arrays
 variable type[ value_1][ value_2]…[ value_n]
Use n []’s for n dimensional array
 Examples
– array_1d[1] = 7;
– array_2d[2][3] = 14;
– array_3d[1][0][2] = 55;
44
Times Table
int[][] times_table = new int[10][10];
for (i = 1; i < 10; i++)
for (j = 1; j < 10; j++)
times_table[i][j] = i * j;
for (i = 1; i < 10; i++) {
System.out.println();
for (j = 1; j < 10; j++)
System.out.print(df.format(times_table[i][j]) + " ");
}
01 02 03 04 05 06 07 08
09
02 04 06 08 10 12 14 16
18
03 06 09 12 15 18 21 24
27
04 08 12 16 20 24 28 32
36
05 10 15 20 25 30 35 40
45
45
// TimesTable - prints a times table using doubly-nested for loops
import java.text.DecimalFormat;
public class Main {
public static void main (String[] args) {
final int X_LIMIT = 10;
int[][] times_table = new int[X_LIMIT][X_LIMIT];
DecimalFormat df = new DecimalFormat("00");
int i,j;
for (i = 1; i < X_LIMIT; i++)
for (j = 1; j < X_LIMIT; j++)
times_table[i][j] = i * j;
for (i = 1; i < X_LIMIT; i++) {
System.out.println();
for (j = 1; j < X_LIMIT; j++)
System.out.print(df.format(times_table[i][j]) + " ");
}
} // main
} // Main
46
array_2d - Who’s on first?
int[][] array_2d;
 array_2d A Pointer to an Array of Pointers
to an Array of int’s
 array_2d[0]
A Pointer to an Array of Int’s
(array_2d)[0]
 array_2d[0][0] An Int
(array_2d[0])[0]
((array_2d)[0])[0]
47
Using array_2d
 int[][] array_2d; // pointer
 array_2d = new int[4][]; // array of 4 pointers
array_2d.length == 4
 array_2d[0] = new int[4]; // array of 4 ints
array_2d[0].length == 4
 array_2d[1] = new int[2]; // array of 2 ints
array_2d[1].length == 2
 array_2d[2] = new int[3]; // array of 3 ints
array_2d[2].length == 3
 array_2d[3] = new int[2]; // array of 2 ints
array_2d[3].length == 2
48
// Multidimensional - multidimensional arrays
import java.text.DecimalFormat;
public class Main {
public static void main (String[] args) {
int[][] array_2d;
array_2d = new int[4][];
array_2d[0] = new int[4];
array_2d[0][0] = 00;
array_2d[0][1] = 01;
array_2d[0][2] = 02;
array_2d[0][3] = 03;
array_2d[1] = new int[2];
array_2d[1][0] = 10;
array_2d[1][1] = 11;
49
array_2d[2] = new int[3];
array_2d[2][0] = 20;
array_2d[2][1] = 21;
array_2d[2][2] = 22;
array_2d[3] = new int[2];
array_2d[3][0] = 30;
array_2d[3][1] = 31;
printArray2D("array_2d", array_2d);
int[] array_1d;
array_1d = array_2d[2];
printArray1D("array_1d", array_1d);
array_1d[0] = 10020;
array_1d[1] = 10021;
array_1d[2] = 10022;
printArray1D("array_1d", array_1d);
printArray1D("array_2d", array_2d[2]);
50
array_2d[2][0] = 20;
array_2d[2][1] = 21;
array_2d[2][2] = 22;
printArray1D("array_1d", array_1d);
printArray1D("array_2d", array_2d[2]);
} // main
public static void printArray2D(String identifier, int[][] array) {
DecimalFormat df = new DecimalFormat("00");
for (int i = 0; i < array.length; i++) {
System.out.print("\n" + identifier);
for (int j = 0; j < array[i].length; j++)
System.out.print(
"[" + i + "]" + "[" + j + "]" +
"(" + df.format(array[i][j]) + ") "
);
}
System.out.println();
} // printArray2D
51
public static void printArray1D(String identifier, int[] array) {
DecimalFormat df = new DecimalFormat("00");
System.out.print("\n" + identifier);
for (int i = 0; i < array.length; i++)
System.out.print(
"[" + i + "]" +
"(" + df.format(array[i]) + ") "
);
System.out.println();
} // printArray1D
array_2d[0][0] (00) [0][1](01) [0][2](02) [0][3](03)
} // main
array_2d[1][0] (10) [1][1](11)
array_2d[2][0] (20) [2][1](21) [2][2](22)
array_2d[3][0] (30) [3][1](31)
array_1d[0] (20) [1](21) [2](22)
array_1d[0] (10020) [1](10021) [2](10022)
array_2d[0] (10020) [1](10021) [2](10022)
array_1d[0] (20) [1](21) [2](22)
array_2d[0] (20) [1](21) [2](22)
52
Declaring array_2d
(A Pointer to an Array of Pointers to an Array of int’s)
Address
int[][] array_2d;
Value
1024 null
1028
Identifier
array_2d
1032
1036
1040
1044
1048
1052
1056
1060
1064
1068
1072
1076
1080
1084
1088
1092
53
Instantiating array_2d
(A Pointer to an Array of Pointers to an Array of int’s)
Address
array_2d = new int[4][];
Value
1024
1028
1028
null
1032
null
1036
null
1040
null
1044
Identifier
array_2d
[0]
[1]
[2]
[3]
1048
1052
1056
1060
1064
1068
1072
1076
1080
1084
1088
1092
54
Instantiating array_2d[0]
(A Pointer to Array of int’s)
Address
array_2d[0] = new int[4][];
Value
Identifier
1024
1028
1028
1044
1032
null
1036
null
1040
null
1044
0
1048
0
1052
0
1056
0
1060
array_2d
[0]
[1]
[2]
[3]
[0]
[1]
[2]
[3]
1064
1068
1072
1076
1080
1084
1088
1092
55
Using array_2d[0]
(A Pointer to Array of int’s)
Address
array_2d[0][0] = 00;
array_2d[0][1] = 01;
array_2d[0][2] = 02;
array_2d[0][3] = 03;
Value
1024
1028
1028
1044
1032
null
1036
null
1040
null
1044
00
1048
01
1052
02
1056
03
1060
Identifier
array_2d
[0]
[1]
[2]
[3]
[0]
[1]
[2]
[3]
1064
1068
1072
1076
1080
1084
1088
1092
56
Intantiating array_2d[1]
(A Pointer to Array of int’s)
Address
array_2d[1] = new int[2];
Value
Identifier
1024
1028
1028
1044
1032
1060
1036
null
1040
null
1044
00
1048
01
1052
02
1056
03
1060
0
1064
0
array_2d
[0]
[1]
[2]
[3]
[0]
[1]
[2]
[3]
[0]
[1]
1068
1072
1076
1080
1084
1088
1092
57
Using array_2d[1]
(A Pointer to Array of int’s)
Address
array_2d[1][0] = 10;
array_2d[1][1] = 11;
Value
1024
1028
1028
1044
1032
1060
1036
null
1040
null
1044
00
1048
01
1052
02
1056
03
1060
10
1064
11
Identifier
array_2d
[0]
[1]
[2]
[3]
[0]
[1]
[2]
[3]
[0]
[1]
1068
1072
1076
1080
1084
1088
1092
58
array_2d[2] and array_2d[3]
(A Pointer to Array of int’s)
Address
array_2d[2] = new int[3];
array_2d[2][0] = 20;
array_2d[2][1] = 21;
array_2d[2][2] = 22;
array_2d[3] = new int[2];
array_2d[3][0] = 30;
array_2d[3][1] = 31;
Value
1024
1028
1028
1044
1032
1060
1036
1068
1040
1080
1044
00
1048
01
1052
02
1056
03
1060
10
1064
11
1068
20
1072
21
1076
22
1080
30
1084
31
Identifier
array_2d
[0]
[1]
[2]
[3]
[0]
[1]
[2]
[3]
[0]
[1]
[0]
[1]
[2]
[0]
[1]
1088
1092
59
Declare array_1d
(A Pointer to Array of int’s)
Address
int[] array_1d;
Value
1024
1028
1028
1044
1032
1060
1036
1068
1040
1080
1044
00
1048
01
1052
02
1056
03
1060
10
1064
11
1068
20
1072
21
1076
22
1080
30
1084
31
1088
null
1092
Identifier
array_2d
[0]
[1]
[2]
[3]
[0]
[1]
[2]
[3]
[0]
[1]
[0]
[1]
[2]
[0]
[1]
array_1d
60
Assigning a Value to array_1d
(A Pointer to Array of int’s)
Address
// Error! Why?
// array_1d = array_2d;
array_1d = array_2d[2];
Value
1024
1028
1028
1044
1032
1060
1036
1068
1040
1080
1044
00
1048
01
1052
02
1056
03
1060
10
1064
11
1068
20
1072
21
1076
22
1080
30
1084
31
1088
null
1092
Identifier
array_2d
[0]
[1]
[2]
[3]
[0]
[1]
[2]
[3]
[0]
[1]
[0]
[1]
[2]
[0]
[1]
array_1d
61
Using array_1d
(A Pointer to Array of int’s)
Address
array_1d[0] = 10020;
array_1d[1] = 10021;
array_1d[2] = 10031;
Value
1024
1028
1028
1044
1032
1060
1036
1068
1040
1080
1044
00
1048
01
1052
02
1056
03
1060
10
1064
11
1068
10020
1072
10021
1076
10031
1080
30
1084
31
1088
1068
1092
Identifier
array_2d
[0]
[1]
[2]
[3]
[0]
[1]
[2]
[3]
[0]
[1]
[0]
[1]
[2]
[0]
[1]
array_1d
62
Using array_2d
(A Pointer to Array of int’s)
Address
array_2d[2][0] = 20;
array_2d[2][1] = 21;
array_2d[2][2] = 22;
Value
1024
1028
1028
1044
1032
1060
1036
1068
1040
1080
1044
00
1048
01
1052
02
1056
03
1060
10
1064
11
1068
20
1072
21
1076
22
1080
30
1084
31
1088
1068
1092
Identifier
array_2d
[0]
[1]
[2]
[3]
[0]
[1]
[2]
[3]
[0]
[1]
[0]
[1]
[2]
[0]
[1]
array_1d
63
Initializing Multidimensional Arrays
 Use Lists of Initializer Lists
 Example
int[][] array_2d = {
{00, 01, 02, 03},
{10, 11},
{20, 21, 22},
{30, 31}
};
 Length
–
–
–
–
–
array_2d.length == 4
array_2d[0].length == 4
array_2d[1].length == 2
array_2d[2].length == 3
array_2d[3].length == 2
64
// Initializer - array initializer list
import java.text.DecimalFormat;
public class Main {
public static void main (String[] args) {
int[][] array_2d = {
{00, 01, 02, 03},
{10, 11},
{20, 21, 22},
{30, 31}
};
for (int i = 0; i < array_2d.length; i++)
System.out.println(
"array_2d[" + i + "].length = " +
array_2d[i].length
);
printArray2D("array_2d", array_2d);
} // main
65
public static void printArray2D(String identifier, int[][] array) {
DecimalFormat df = new DecimalFormat("00");
for (int i = 0; i < array.length; i++) {
System.out.print("\n" + identifier);
for (int j = 0; j < array[i].length; j++)
System.out.print(
"[" + i + "]" + "[" + j + "]" +
"(" + df.format(array[i][j]) + ") "
);
}
System.out.println(); array_2d[0].length = 4
array_2d[1].length = 2
} // printArray2D
array_2d[2].length = 3
} // Main
array_2d[3].length = 2
array_2d[0][0](00) [0][1](01) [0][2](02)
[0][3](03)
array_2d[1][0](10) [1][1](11)
array_2d[2][0](20) [2][1](21) [2][2](22)
array_2d[3][0](30) [3][1](31) 68
66
Primitive vs. Object Parameters
 All parameters are passed by value.
Value of actual parameter copied to local parameter
 Primitive
– Value Copied? Value of primitive type
– Can change value of local copy (of primitive type)
– Cannot access actual parameter
 Object
–
–
–
–
Value Copied? Reference (address) of object
Can change value of local copy (of object address)
Cannot access actual parameter
Can access object pointed to by actual parameter
67
Arrays as Parameters
 Objects may be passed as parameters.
 Arrays…
– ...are objects.
– …may be passed as parameters.
 “Value” of an Array Variable
– Address of array
– Passed to methods
68
// Parameters - arrays as parameters
import java.text.DecimalFormat;
public class Main {
static DecimalFormat df = new DecimalFormat("0000");
final static int I = 1;
final static int J = 2;
public static void main (String[] args) {
int[][] array_2d = {
{00, 01, 02},
{10, 11, 12},
};
69
System.out.println("println 1: " + df.format(array_2d[I][J]));
paramArray2D(array_2d);
System.out.println("println 5: " + df.format(array_2d[I][J]));
paramArray1D(array_2d[I]);
System.out.println("println 9: " + df.format(array_2d[I][J]));
paramInt(array_2d[I][J]);
System.out.println("println 12: " + df.format(array_2d[I][J]));
} // main
println 1: 0012
println 2: 0012
println 3: 0112
println 4: 9999
println 5: 0112
println 6: 0112
println 7: 1112
println 8: 9999
println 9: 1112
println 10: 1112
println 11: 9999
println 12: 1112 72
70
public static void paramArray2D(int param_2d[][]) {
System.out.println("println 2: " + df.format(param_2d[I][J]));
param_2d[I][J] += 100;
System.out.println("println 3: " + df.format(param_2d[I][J]));
param_2d = new int[I + 1][J + 1];
param_2d[I][J] = 9999;
System.out.println("println 4: " + df.format(param_2d[I][J]));
} // paramArray2D
println 1: 0012
println 2: 0012
println 3: 0112
println 4: 9999
println 5: 0112
println 6: 0112
println 7: 1112
println 8: 9999
println 9: 1112
println 10: 1112
println 11: 9999
println 12: 1112
71
public static void paramInt(int param_int) {
System.out.println("println 10: " + df.format(param_int));
param_int = 9999;
System.out.println("println 11: " + df.format(param_int));
} // paramInt
} // Main
println 1: 0012
println 2: 0012
println 3: 0112
println 4: 9999
println 5: 0112
println 6: 0112
println 7: 1112
println 8: 9999
println 9: 1112
println 10: 1112
println 11: 9999
println 12: 1112
72
public static void paramArray1D(int param_1d[]) {
System.out.println("println 6: " + df.format(param_1d[J]));
param_1d[J] += 1000;
System.out.println("println 7: " + df.format(param_1d[J]));
param_1d = new int[J + 1];
param_1d[J] = 9999;
System.out.println("println 8: " + df.format(param_1d[J]));
} // paramArray1D
println 1: 0012
println 2: 0012
println 3: 0112
println 4: 9999
println 5: 0112
println 6: 0112
println 7: 1112
println 8: 9999
println 9: 1112
println 10: 1112
println 11: 9999
println 12: 1112
73
Array Parameter (Parameters.java)
Address
int[][] array_2d = {
{00, 01, 02},
{10, 11, 12},
};
System.out.println(
"println 1: " +
array_2d[1][2]
);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
12
1060
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
1064
1068
1072
1076
1080
println 1: 0012
1084
1088
1092
74
Invoking paramArray2D()
(array_2d -> param_2d)
Address
paramArray2D(array_2d);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
12
1060
1028
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
param_2d
1064
1068
1072
1076
1080
1084
1088
1092
75
Executing paramArray2D()
Address
System.out.println(
"println 2: " +
param_2d[1][2]
);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
12
1060
1028
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
param_2d
1064
1068
1072
1076
println 2: 0012
1080
1084
1088
1092
76
Executing paramArray2D()
Address
param_2d[1][2] += 100;
System.out.println(
"println 3: " +
param_2d[1][2]
);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
112
1060
1028
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
param_2d
1064
1068
1072
1076
println 3: 0112
1080
1084
1088
1092
77
Executing paramArray2D()
Address
param_2d = new int[2][3];
Value
Identifier
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
112
1060
1064
1064
1072
1068
1084
1072
0
1076
0
1080
0
1084
0
1088
0
1092
0
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
param_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
78
Executing paramArray2D()
Address
param_2d[1][2] = 9999;
System.out.println(
"println 4: " +
param_2d[1][2]
);
println 4: 9999
Value
Identifier
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
112
1060
1064
1064
1072
1068
1084
1072
0
1076
0
1080
0
1084
0
1088
0
1092
9999
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
param_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
79
Returning to main()
Address
System.out.println(
"println 5: " +
array_2d[1][2]
);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
112
1060
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
1064
1068
1072
1076
println 5: 0112
1080
1084
1088
1092
80
Invoking paramArray1D()
(array_2d[1] -> param_1d)
Address
paramArray1D(array_2d[1]);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
112
1060
1048
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
param_1d
1064
1068
1072
1076
1080
1084
1088
1092
81
Executing paramArray1D()
Address
System.out.println(
"println 6: " +
param_1d[2]
);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
112
1060
1048
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
param_1d
1064
1068
1072
1076
println 6: 0112
1080
1084
1088
1092
82
Executing paramArray1D()
Address
param_1d[2] += 1000;
System.out.println(
"println 7: " +
param_1d[2]
);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
1112
1060
1048
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
param_1d
1064
1068
1072
1076
println 7: 1112
1080
1084
1088
1092
83
Executing paramArray1D()
Address
param_1d = new int[3];
Value
Identifier
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
1112
1060
1064
1064
0
1068
0
1072
0
1076
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
param_1d
[0]
[1]
[2]
1080
1084
1088
1092
84
Executing paramArray1D()
Address
param_1d[2] = 9999;
System.out.println(
"println 8: " +
param_1d[2]
);
Identifier
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
1112
1060
1064
1064
0
1068
0
1072
9999
1076
println 8: 9999
Value
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
param_1d
[0]
[1]
[2]
1080
1084
1088
1092
85
Returning to main()
Address
System.out.println(
"println 9: " +
array_2d[1][2]
);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
1112
1060
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
1064
1068
1072
1076
println 9: 1112
1080
1084
1088
1092
86
Invoking paramInt()
(array_2d[1][2] -> param_int)
Address
paramInt(array_2d[1][2]);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
1112
1060
1112
1064
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
para_int
1068
1072
1076
1080
1084
1088
1092
87
Executing paramInt()
Address
System.out.println(
"println 10: " +
param_int
);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
1112
1060
1112
1064
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
para_int
1068
1072
1076
println 10: 1112
1080
1084
1088
1092
88
Executing paramInt()
Address
param_int = 9999;
System.out.println(
"println 11: " +
param_int
);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
1112
1060
9999
1064
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
para_int
1068
1072
1076
println 11: 9999
1080
1084
1088
1092
89
Executing paramInt()
Address
System.out.println(
"println 12: " +
array_2d[1][2]
);
Value
1024
1028
1028
1036
1032
1048
1036
00
1040
01
1044
02
1048
10
1052
11
1056
1112
1060
Identifier
array_2d
[0]
[1]
[0]
[1]
[2]
[0]
[1]
[2]
1064
1068
1072
1076
println 12: 1112
1080
1084
1088
1092
90