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2010-06-01T05:20:51Z

1 версия

в 17:44, 31 мая 2010

2010-05-31T17:44:27Z

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== Constraints on a Wildcard ==



<source lang="java">
public static void saveAll(LinkedList<? extends java.io.Serializable> list) {

}
public static void analyze(LinkedList<? super MyClass> list) {

}</source>



== Multiple Type Parameters ==



<source lang="java">
class Pair<KeyType, ValueType> {
// Constructor
public Pair(KeyType aKey, ValueType aValue) {
key = aKey;
value = aValue;
}
// Get the key for this pair
public KeyType getKey() {
return key;
}
// Get the value for this pair
public ValueType getValue() {
return value;
}
// Set the value for this pair
public void setValue(ValueType aValue) {
value = aValue;
}
private KeyType key;
private ValueType value;
}
public class MainClass {
public static void main(String[] a) {
Pair<Integer, String> p = new Pair<Integer, String>(1, "A");
System.out.println(p.getKey().getClass().getName());
}
}</source>



<pre class=codeResult>java.lang.Integer</pre>

== Type Parameter Bounds ==



<source lang="java">
import static java.lang.Math.random;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

public class MainClass {
public static void main(String[] args) throws Exception {
LinkedList<Integer> numbers = new LinkedList<Integer>();
for (int i = 0; i < 10; i++) {
numbers.addItem(1 + (int) (100.0 * random()));
}
System.out.println("\nnumbers list contains:");
listAll(numbers);
String filename = "C:/Numbers.bin";
ObjectOutputStream objOut = new ObjectOutputStream(new FileOutputStream(filename));
objOut.writeObject(numbers);
objOut.close();
LinkedList<Integer> values = null;
ObjectInputStream objIn = new ObjectInputStream(new FileInputStream(filename));
values = (LinkedList<Integer>) (objIn.readObject());
objIn.close();
System.out.println("\nvalues list contains:");
listAll(values);
}
static void listAll(LinkedList<Integer> list) {
Integer number = list.getFirst();
int count = 0;
do {
System.out.printf("%5d", number);
if (++count % 5 == 0) {
System.out.println();
}
} while ((number = list.getNext()) != null);
}
}</source>



<pre class=codeResult>numbers list contains:
39 63 34 47 86
88 21 39 40 1
values list contains:
39 63 34 47 86
88 21 39 40 1</pre>

== Using Bounded Wildcards in Methods ==

<p>The syntax for using an upper bound is as follows:</p>



<source lang="java">
GenericType<? extends upperBoundType></source>



<pre class=codeResult>111.0
18.0</pre>

== Using the ? wildcard ==



<source lang="java">
import java.util.ArrayList;
import java.util.List;
public class MainClass {
public static void printList (List<?> list) {
for (Object element : list) {
System.out.println(element);
}
}
public static void main(String[] args) {
List<String> list1 = new ArrayList<String>();
list1.add ("Hello");
list1.add ("World");
printList (list1);
List<Integer> list2 = new ArrayList<Integer>();
list2.add(100);
list2.add(200);
printList(list2);
}
}</source>



<pre class=codeResult>Hello
World
100
200</pre>

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Admin: 1 версия

в 17:44, 31 мая 2010