Capitulo 1 de java array unidimensionales

Liang, Introduction to Java Programming, Sixth Edition, (c) 2007 Pearson Education, Inc. All
rights reserved. 0-13-222158-6
Chapter 5
Arrays
1

Introducing Arrays
2
Array is a data structure that represents a collection of the
same types of data.
5.6
4.5
3.3
13.2
4
34.33
34
45.45
99.993
11123
double[] myList = new double[10];
myList reference
myList[0]
myList[1]
myList[2]
myList[3]
myList[4]
myList[5]
myList[6]
myList[7]
myList[8]
myList[9]
Element value
Array reference
variable
Array element at
index 5

Declaring Array Variables
• datatype[] arrayRefVar;
Example:
double[] myList;
3

Creating Arrays
arrayRefVar = new datatype[arraySize];
Example:
myList = new double[10];
myList[0] references the first element in the array.
myList[9] references the last element in the array.
4

Declaring and Creating in One Step
• datatype[] arrayRefVar = new datatype[arraySize];
Example:
5

The Length of an Array
Once an array is created, its size is fixed. It cannot be
changed. You can find its size using
arrayRefVar.length
For example,
myList.length returns 10
6

Default Values
When an array is created, its elements are
assigned the default value of
0 for the numeric primitive data types,
'u0000' for char types, and
false for boolean types.
7

Indexed Variables
The array elements are accessed through the index.
The array indices are 0-based, i.e., it starts from 0 to
arrayRefVar.length-1. In the example in Figure 6.1,
myList holds ten double values and the indices are
from 0 to 9.
Each element in the array is represented using the
following syntax, known as an indexed variable:
arrayRefVar[index];
8

Using Indexed Variables
After an array is created, an indexed variable
can be used in the same way as a regular
variable. For example, the following code adds
the value in myList[0] and myList[1] to
myList[2].
myList[2] = myList[0] + myList[1];
9

Declaring, creating, initializing Using the
Shorthand Notation
double[] myList = {1.9, 2.9, 3.4, 3.5};
This shorthand notation is equivalent to the following
statements:
myList[0] = 1.9;
myList[1] = 2.9;
myList[2] = 3.4;
myList[3] = 3.5;
10

CAUTION
Using the shorthand notation, you have to declare, create,
and initialize the array all in one statement. Splitting it
would cause a syntax error. For example, the following is
wrong:
double[] myList;
myList = {1.9, 2.9, 3.4, 3.5};
11

Trace Program with Arrays
int[] values = new int[5];
for (int i = 1; i < 5; i++)
{
values[i] = i + values[i-1];
}
values[0] = values[1] + values[4];
12
Declare array variable values, create an
array, and assign its reference to values
After the array is created
0
1
2
3
4
0
0
0
0
0
animation

for (int i = 1; i < 5; i++)
{
}
13
i becomes 1
animation
0
1
2
3
4
0
0
0
0
0

for (int i = 1; i < 5; i++)
{
}
14
i (=1) is less than 5
animation
0
1
2
3
4
0
0
0
0
0

for (int i = 1; i < 5; i++)
{
}
15
After this line is executed, value[1] is 1
After the first iteration
0
1
2
3
4
0
1
0
0
0
animation

for (int i = 1; i < 5; i++)
{
}
16
After i++, i becomes 2
animation
0
1
2
3
4
0
1
0
0
0

for (int i = 1; i < 5; i++)
{
}
17
i (= 2) is less than 5
animation
0
1
2
3
4
0
1
0
0
0

for (int i = 1; i < 5; i++)
{
}
18
After this line is executed,
values[2] is 3 (2 + 1)
After the second iteration
0
1
2
3
4
0
1
3
0
0
animation

for (int i = 1; i < 5; i++)
{
}
19
After this, i becomes 3
animation
0
1
2
3
4
0
1
3
0
0

for (int i = 1; i < 5; i++)
{
}
20
i (=3) is still less than 5.
animation
0
1
2
3
4
0
1
3
0
0

for (int i = 1; i < 5; i++)
{
}
21
After this line, values[3] becomes 6 (3 + 3)
After the third iteration
0
1
2
3
4
0
1
3
6
0
animation

for (int i = 1; i < 5; i++)
{
}
22
After this, i becomes 4
0
1
2
3
4
0
1
3
6
0
animation

for (int i = 1; i < 5; i++)
{
}
23
i (=4) is still less than 5
0
1
2
3
4
0
1
3
6
0
animation

for (int i = 1; i < 5; i++)
{
}
24
After this, values[4] becomes 10 (4 + 6)
After the fourth iteration
0
1
2
3
4
0
1
3
6
10
animation

for (int i = 1; i < 5; i++)
{
}
25
After i++, i becomes 5
animation
0
1
2
3
4
0
1
3
6
10

for (int i = 1; i < 5; i++)
{
}
26
i ( =5) < 5 is false. Exit the loop
animation
0
1
2
3
4
0
1
3
6
10

for (int i = 1; i < 5; i++)
{
}
27
After this line, values[0] is 11 (1 + 10)
0
1
2
3
4
11
1
3
6
10
animation

Processing Arrays
See the examples in the text.
1. (Initializing arrays)
2. (Printing arrays)
3. (Summing all elements)
4. (Finding the largest element)
5. (Finding the smallest index of the largest
element)
28

Copying Arrays (incorrect way)
Often, in a program, you need to duplicate an array or a part of an
array. In such cases you could attempt to use the assignment
statement (=), as follows:
list2 = list1;
29
Contents
of list1
list1
Contents
of list2
list2
Before the assignment
list2 = list1;
Contents
of list1
list1
Contents
of list2
list2
After the assignment
list2 = list1;
Garbage

Copying Arrays (correct way)
Using a loop:
int[] sourceArray = {2, 3, 1, 5, 10};
int[] targetArray = new int[sourceArray.length];
for (int i = 0; i < sourceArrays.length; i++)
targetArray[i] = sourceArray[i];
30

Example: Largest Number
• Objective: The program receives 6 numbers from
the user, finds the largest number and counts the
occurrence of the largest number entered.
Suppose you entered 3, 5, 2, 5, 5, and 5, the
largest number is 5 and its occurrence count is 4.
31

Example: Assigning Grades
• Objective: read student scores (int), get the best
score, and then assign grades based on the
following scheme:
• Grade is A if score is >= best–10;
• Grade is B if score is >= best–20;
• Grade is C if score is >= best–30;
• Grade is D if score is >= best–40;
• Grade is F otherwise.
32

Capitulo 1 de java array unidimensionales

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