Java Tutorial/Generics/Generic Class
Содержание
Defining a Generic Class Type
<source lang="java">
import java.awt.Point; class ListItem {
public ListItem(Object item) {
this.item = item;
next = null;
}
public String toString() {
return "ListItem " + item;
}
ListItem next;
Object item;
} class LinkedList<T> {
public LinkedList() {
}
public LinkedList(T item) {
if (item != null) {
current = end = start = new ListItem(item);
}
}
public LinkedList(T[] items) {
if (items != null) {
for (int i = 0; i < items.length; i++) {
addItem(items[i]);
}
current = start;
}
}
public void addItem(T item) {
ListItem newEnd = new ListItem(item);
if (start == null) {
start = end = newEnd;
} else {
end.next = newEnd;
end = newEnd;
}
}
public T getFirst() {
current = start;
return start == null ? null : start.item;
}
public T getNext() {
if (current != null) {
current = current.next;
}
return current == null ? null : current.item;
}
private ListItem start = null;
private ListItem end = null;
private ListItem current = null;
private class ListItem {
public ListItem(T item) {
this.item = item;
next = null;
}
public String toString() {
return "ListItem " + item;
}
ListItem next;
T item;
}
} public class MainClass {
public static void main(String[] a) {
LinkedList<Point> polyline = new LinkedList<Point>();
polyline.addItem(new Point(1, 2));
polyline.addItem(new Point(2, 3));
Point p = polyline.getFirst();
System.out.println(p);
}
}</source>
java.awt.Point[x=1,y=2]
Generic class Stack
<source lang="java">
class Stack<E> {
private final int size;
private int top;
private E[] elements;
public Stack() {
this(10);
}
public Stack(int s) {
size = s > 0 ? s : 10;
top = -1;
elements = (E[]) new Object[size]; // create array
}
public void push(E pushValue) {
if (top == size - 1) // if stack is full
throw new FullStackException(String.format("Stack is full, cannot push %s", pushValue));
elements[++top] = pushValue; // place pushValue on Stack
}
public E pop() {
if (top == -1) // if stack is empty
throw new EmptyStackException("Stack is empty, cannot pop");
return elements[top--]; // remove and return top element of Stack
}
} class EmptyStackException extends RuntimeException {
public EmptyStackException() {
this("Stack is empty");
}
public EmptyStackException(String exception) {
super(exception);
}
} class FullStackException extends RuntimeException {
public FullStackException() {
this("Stack is full");
}
public FullStackException(String exception) {
super(exception);
}
} public class MainClass {
public static void main(String args[]) {
double[] doubleElements = { 1.1, 2.2, 3.3, 4.4, 5.5, 6.6 };
int[] integerElements = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };
Stack<Double> doubleStack = new Stack<Double>(5);
Stack<Integer> integerStack = new Stack<Integer>(10);
// test Push Double
try {
System.out.println("\nPushing elements onto doubleStack");
for (double element : doubleElements) {
System.out.printf("%.1f ", element);
doubleStack.push(element);
}
} catch (FullStackException fullStackException) {
System.err.println();
fullStackException.printStackTrace();
}
// test Pop Double
try {
System.out.println("\nPopping elements from doubleStack");
double popValue;
while (true) {
popValue = doubleStack.pop(); // pop from doubleStack
System.out.printf("%.1f ", popValue);
}
} catch (EmptyStackException emptyStackException) {
System.err.println();
emptyStackException.printStackTrace();
}
// test push method with integer stack
try {
System.out.println("\nPushing elements onto integerStack");
for (int element : integerElements) {
System.out.printf("%d ", element);
integerStack.push(element);
}
} catch (FullStackException fullStackException) {
System.err.println();
fullStackException.printStackTrace();
}
// test pop method with integer stack
try {
System.out.println("\nPopping elements from integerStack");
int popValue; // store element removed from stack
// remove all elements from Stack
while (true) {
popValue = integerStack.pop();
System.out.printf("%d ", popValue);
}
} catch (EmptyStackException emptyStackException) {
System.err.println();
emptyStackException.printStackTrace();
}
}
}</source>
Raw type test for a generic Stack
<source lang="java">
class Stack<E> {
private final int size;
private int top;
private E[] elements;
public Stack() {
this(10);
}
public Stack(int s) {
size = s > 0 ? s : 10;
top = -1;
elements = (E[]) new Object[size]; // create array
}
public void push(E pushValue) {
if (top == size - 1) // if stack is full
throw new FullStackException(String.format("Stack is full, cannot push %s", pushValue));
elements[++top] = pushValue; // place pushValue on Stack
}
public E pop() {
if (top == -1) // if stack is empty
throw new EmptyStackException("Stack is empty, cannot pop");
return elements[top--]; // remove and return top element of Stack
}
} class EmptyStackException extends RuntimeException {
public EmptyStackException() {
this("Stack is empty");
}
public EmptyStackException(String exception) {
super(exception);
}
} class FullStackException extends RuntimeException {
public FullStackException() {
this("Stack is full");
}
public FullStackException(String exception) {
super(exception);
}
} public class MainClass {
private static Double[] doubleElements = { 1.1, 2.2, 3.3, 4.4, 5.5, 6.6 };
private static Integer[] integerElements = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };
// generic method pushes elements onto stack
public static <T> void testPush(String name, Stack<T> stack, T[] elements) {
try {
System.out.printf("\nPushing elements onto %s\n", name);
for (T element : elements) {
System.out.printf("%s ", element);
stack.push(element);
}
} catch (FullStackException fullStackException) {
System.out.println();
fullStackException.printStackTrace();
}
}
// generic method testPop pops elements from stack
public static <T> void testPop(String name, Stack<T> stack) {
try {
System.out.printf("\nPopping elements from %s\n", name);
T popValue;
while (true) {
popValue = stack.pop();
System.out.printf("%s ", popValue);
}
} catch (EmptyStackException emptyStackException) {
System.out.println();
emptyStackException.printStackTrace();
}
}
public static void main(String args[]) {
Stack rawTypeStack1 = new Stack(5);
Stack rawTypeStack2 = new Stack<Double>(5);
Stack<Integer> integerStack = new Stack(10);
testPush("rawTypeStack1", rawTypeStack1, doubleElements);
testPop("rawTypeStack1", rawTypeStack1);
testPush("rawTypeStack2", rawTypeStack2, doubleElements);
testPop("rawTypeStack2", rawTypeStack2);
testPush("integerStack", integerStack, integerElements);
testPop("integerStack", integerStack);
}
}</source>
The Run-Time Types of Generic Type Instances
<source lang="java">
import java.util.LinkedList; public class MainClass {
public static void main(String[] args) {
LinkedList<String> proverbs = new LinkedList<String>();
LinkedList<Double> numbers = new LinkedList<Double>();
System.out.println("numbers class name " + numbers.getClass().getName());
System.out.println("proverbs class name " + proverbs.getClass().getName());
System.out.println("Compare Class objects: " + numbers.getClass().equals(proverbs.getClass()));
}
}</source>
numbers class name java.util.LinkedList proverbs class name java.util.LinkedList Compare Class objects: true
Use generic method to test generic Stack
<source lang="java">
// Generic class Stack. class Stack<E> {
private final int size;
private int top;
private E[] elements;
public Stack() {
this(10);
}
public Stack(int s) {
size = s > 0 ? s : 10;
top = -1;
elements = (E[]) new Object[size]; // create array
}
public void push(E pushValue) {
if (top == size - 1) // if stack is full
throw new FullStackException(String.format("Stack is full, cannot push %s", pushValue));
elements[++top] = pushValue; // place pushValue on Stack
}
public E pop() {
if (top == -1) // if stack is empty
throw new EmptyStackException("Stack is empty, cannot pop");
return elements[top--]; // remove and return top element of Stack
}
} class EmptyStackException extends RuntimeException {
public EmptyStackException() {
this("Stack is empty");
}
public EmptyStackException(String exception) {
super(exception);
}
} class FullStackException extends RuntimeException {
public FullStackException() {
this("Stack is full");
}
public FullStackException(String exception) {
super(exception);
}
} public class MainClass {
private static Double[] doubleElements = { 1.1, 2.2, 3.3, 4.4, 5.5, 6.6 };
private static Integer[] integerElements = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 };
private static Stack<Double> doubleStack = new Stack<Double>(5); // Stack of
// Doubles
private static Stack<Integer> integerStack = new Stack<Integer>(10); // Stack
// of
// Integers
// generic method testPush pushes elements onto a Stack
public static <T> void testPush(String name, Stack<T> stack, T[] elements) {
try {
System.out.printf("\nPushing elements onto %s\n", name);
for (T element : elements) {
System.out.printf("%s ", element);
stack.push(element);
}
} catch (FullStackException fullStackException) {
System.out.println();
fullStackException.printStackTrace();
}
}
// generic method testPop pops elements from a Stack
public static <T> void testPop(String name, Stack<T> stack) {
try {
System.out.printf("\nPopping elements from %s\n", name);
T popValue;
while (true) {
popValue = stack.pop();
System.out.printf("%s ", popValue);
}
} catch (EmptyStackException emptyStackException) {
System.out.println();
emptyStackException.printStackTrace();
}
}
public static void main(String args[]) {
testPush("doubleStack", doubleStack, doubleElements);
testPop("doubleStack", doubleStack);
testPush("integerStack", integerStack, integerElements);
testPop("integerStack", integerStack);
}
}</source>
Using Primitive Type Wrapper Class Types as Arguments
<source lang="java">
class ListItem {
public ListItem(Object item) {
this.item = item;
next = null;
}
public String toString() {
return "ListItem " + item;
}
ListItem next;
Object item;
} class LinkedList<T> {
public LinkedList() {
}
public LinkedList(T item) {
if (item != null) {
current = end = start = new ListItem(item);
}
}
public LinkedList(T[] items) {
if (items != null) {
for (int i = 0; i < items.length; i++) {
addItem(items[i]);
}
current = start;
}
}
public void addItem(T item) {
ListItem newEnd = new ListItem(item);
if (start == null) {
start = end = newEnd;
} else {
end.next = newEnd;
end = newEnd;
}
}
public T getFirst() {
current = start;
return start == null ? null : start.item;
}
public T getNext() {
if (current != null) {
current = current.next;
}
return current == null ? null : current.item;
}
private ListItem start = null;
private ListItem end = null;
private ListItem current = null;
private class ListItem {
public ListItem(T item) {
this.item = item;
next = null;
}
public String toString() {
return "ListItem " + item;
}
ListItem next;
T item;
}
} public class MainClass {
public static void main(String[] args) {
LinkedList<Double> temperatures = new LinkedList<Double>();
// Insert 6 temperature values 0 to 25 degress Centigrade
for (int i = 0; i < 6; i++) {
temperatures.addItem(25.0 * Math.random());
}
System.out.printf("%.2f degrees Fahrenheit%n", toFahrenheit(temperatures.getFirst()));
Double value = null;
while ((value = temperatures.getNext()) != null) {
System.out.printf("%.2f degrees Fahrenheit%n", toFahrenheit(value));
}
}
// Convert Centigrade to Fahrenheit
public static double toFahrenheit(double temperature) {
return 1.8 * temperature + 32.0;
}
}</source>
69.27 degrees Fahrenheit 51.55 degrees Fahrenheit 59.97 degrees Fahrenheit 35.82 degrees Fahrenheit 41.28 degrees Fahrenheit 37.99 degrees Fahrenheit
