Java Tutorial/Generics/Generic Parameters
Содержание
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>
java.lang.Integer
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>
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
Using Bounded Wildcards in Methods
The syntax for using an upper bound is as follows:
<source lang="java">
GenericType<? extends upperBoundType></source>
111.0 18.0
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>
Hello World 100 200
