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2010-06-01T05:04:45Z

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в 17:44, 31 мая 2010

2010-05-31T17:44:27Z

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== Alternative Array Declaration Syntax ==

For example, the following two declarations are equivalent:



<source lang="java">
int al[] = new int[3];
int[] a2 = new int[3];</source>



== An array is a Java object ==



<source lang="java">
public class MainClass {
static String[] names;
public static void main(String[] a) {
if (names == null) {
System.out.println("true");
} else {
System.out.println("false");
}
}
}</source>



<pre class=codeResult>true</pre>

== Anonymous arrays are declared similarly to regular arrays ==



<source lang="java">
new type[] {comma-delimited-list}</source>



<pre class=codeResult>1
2
3
4
5</pre>

== Array Reallocation ==

You can make a clone of an array and make the new array have a different size.



<source lang="java">
public static boolean[] copyOf (boolean[] original, int newLength)
public static byte[] copyOf (byte[] original, int newLength)
public static char[] copyOf (char[] original, int newLength)
public static double[] copyOf (double[] original, int newLength)
public static float [] copyOf (float[] original, int newLength)
public static int[] copyOf (int[] original, int newLength)
public static long[] copyOf (long[] original, int newLength)
public static short[] copyOf (short[] original, int newLength)
public static <T> T[] copyOf (T[] original, int newLength)
public static <T,U> T[] copyOf (U[] original, int newLength,java.lang.Class<? extends T[]> newType)</source>



<pre class=codeResult>[1, 3, 5, 7, 9]
[1, 3, 5, 7, 9, 11]
[5, 7, 9, 0, 0, 0, 0, 0]</pre>

== Arrays of Characters ==



<source lang="java">
public class MainClass{
public static void main(String[] arg){
char[] message = new char[50];
java.util.Arrays.fill(message, "A");
for(char ch: message){
System.out.println(ch);
}
}
}</source>



<pre class=codeResult>A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A</pre>

== Changing Array Size ==

Once an array is created, its size cannot be changed.
If you want to change the size, you must create a new array and populates it using the values of the old array.



<source lang="java">
public class MainClass {
public static void main(String[] args) {
int[] numbers = { 1, 2, 3 };
int[] temp = new int[4];
int length = numbers.length;
for (int j = 0; j < length; j++) {
temp[j] = numbers[j];
}
numbers = temp;
}
}</source>



== Circular Buffer ==



<source lang="java">
public class TestCircularBuffer {
public static void main(String args[]) {
TestCircularBuffer t = new TestCircularBuffer();
}
public TestCircularBuffer() {
CircularBuffer c = new CircularBuffer(8);
System.out.println("Storing: 1");
c.store(1);
System.out.println("Reading: " + c.read());
System.out.println("Storing: 2");
c.store(2);
System.out.println("Storing: 3");
c.store(3);
System.out.println("Storing: 4");
c.store(4);
System.out.println("Reading: " + c.read());
System.out.println("Reading: " + c.read());
System.out.println("Storing: 8");
c.store(8);
System.out.println("Storing: 9");
c.store(9);
System.out.println("Storing: 10");
c.store(10);
System.out.println("Storing: 11");
c.store(11);
System.out.println("Storing: 12");
c.store(12);
System.out.println("Reading: " + c.read());
System.out.println("Reading: " + c.read());
System.out.println("Reading: " + c.read());
System.out.println("Reading: " + c.read());
System.out.println("Reading: " + c.read());
System.out.println("Reading: " + c.read());
System.out.println("Reading: " + c.read());
System.out.println("Reading: " + c.read());
}
}
class CircularBuffer {
private Integer data[];
private int head;
private int tail;
public CircularBuffer(Integer number) {
data = new Integer[number];
head = 0;
tail = 0;
}
public boolean store(Integer value) {
if (!bufferFull()) {
data[tail++] = value;
if (tail == data.length) {
tail = 0;
}
return true;
} else {
return false;
}
}
public Integer read() {
if (head != tail) {
int value = data[head++];
if (head == data.length) {
head = 0;
}
return value;
} else {
return null;
}
}
private boolean bufferFull() {
if (tail + 1 == head) {
return true;
}
if (tail == (data.length - 1) && head == 0) {
return true;
}
return false;
}
}</source>



== How to define an Array ==

<OL><LI>An array is a named set of same-type variables.</LI><LI>Each variable in the array is called an array element.</LI><LI>The first element will have an index of 0.</LI></OL>



<source lang="java">
public class MainClass {
public static void main(String[] arg) {
int[] intArray = new int[10];
for (int i = 0; i < 10; i++) {
intArray[i] = 100;
}
for (int i = 0; i < 10; i++) {
System.out.println(intArray[i]);
}
}
}</source>



<pre class=codeResult>100
100
100
100
100
100
100
100
100
100</pre>

== Initializing array elements by index ==



<source lang="java">
public class MainClass {
public static void main(String args[]) {
int month_days[];
month_days = new int[12];
month_days[0] = 31;
month_days[1] = 28;
month_days[2] = 31;
month_days[3] = 30;
month_days[4] = 31;
month_days[5] = 30;
month_days[6] = 31;
month_days[7] = 31;
month_days[8] = 30;
month_days[9] = 31;
month_days[10] = 30;
month_days[11] = 31;
System.out.println("April has " + month_days[3] + " days.");
}
}</source>



<pre class=codeResult>April has 30 days.</pre>

== Initializing Arrays ==



<source lang="java">
public class MainClass{
public static void main(String[] arg){
int[] primes = {2, 3, 5, 7, 11, 13, 17}; // An array of 7 elements

for (int i = 0; i < primes.length; i++) {
System.out.println(primes[i]);
}
}
}</source>



<pre class=codeResult>2
3
5
7
11
13
17</pre>

== Merge (or add) two arrays into one ==



<source lang="java">
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class Main {
public static void main(String args[]) {
String a[] = { "a", "b", "c" };
String b[] = { "d", "e" };
List<String> list = new ArrayList<String>(Arrays.asList(a));
list.addAll(Arrays.asList(b));
Object[] c = list.toArray();
System.out.println(Arrays.toString(c));
}
}</source>



== The Length of an Array ==



<source lang="java">
public class MainClass {
public static void main(String[] arg) {
int[] intArray = new int[10];
for (int i = 0; i < intArray.length; i++) {
intArray[i] = 100;
}
for (int i = 0; i < intArray.length; i++) {
System.out.println(intArray[i]);
}
}
}</source>



<pre class=codeResult>100
100
100
100
100
100
100
100
100
100</pre>

== To reference the components of an array ==

To reference the components of an array, use an index after the variable name.
For example, the following snippet creates an array of four String objects and initializes its first member.



<source lang="java">
public class MainClass {
public static void main(String[] args) {
String[] names = new String[4];
names[0] = "Hello World";
}
}</source>



== Use System.arraycopy to duplicate array ==



<source lang="java">
/*
* Copyright (c) 1995 - 2008 Sun Microsystems, Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* - Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* - Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* - Neither the name of Sun Microsystems nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
* IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
* LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
* NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
* SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
public class ArrayCopyDemo {
public static void main(String[] args) {
char[] copyFrom = { "d", "e", "c", "a", "f", "f", "e", "i", "n", "a", "t",
"e", "d" };
char[] copyTo = new char[7];
System.arraycopy(copyFrom, 2, copyTo, 0, 7);
System.out.println(new String(copyTo));
}
}</source>



== Using a for loop to iterate over all the elements and set the values ==



<source lang="java">
public class MainClass {
public static void main(String[] arg) {
double[] data = new double[50]; // An array of 50 values of type double
for (int i = 0; i < data.length; i++) { // i from 0 to data.length-1
data[i] = 1.0;
}

for (int i = 0; i < data.length; i++) { // i from 0 to data.length-1
System.out.println(data[i]);
}

}
}</source>



<pre class=codeResult>1.0
1.0
1.0
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1.0
1.0
1.0
1.0</pre>

== Using the Collection-Based for Loop with an Array ==

You can now use it to iterate over an array or a collection without the index.
Use this syntax to iterate over an array:



<source lang="java">
for (componentType variable: arrayName)</source>



<pre class=codeResult>1.0
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Java Tutorial/Collections/Array Basics - История изменений

Admin: 1 версия

в 17:44, 31 мая 2010