实现固定长度的java.util.Queue 要求实现java.util.Queue<E>。1: 支持范型2:支持固定size。当queue的满了之后插入元素的时候,最先入队的元素要自动remove。 解决方案 » 免费领取超大流量手机卡,每月29元包185G流量+100分钟通话, 中国电信官方发货 你拿ArrayList模拟下不就差不多了自己设置个size,当大于这个size的时候用list的remove方法把第一个去除,全部元素会前移,然后你再插入~ 用滚动数组实现吧public class FixedSizeQueue<E> { Object[] elements; int capacity; int head; int tail; int size; public FixedSizeQueue(int capacity) { if (capacity < 0) throw new IllegalArgumentException("Illegal Capacity: " + capacity); elements = new Object[capacity]; this.capacity = capacity; head = 0; tail = (head - 1) % capacity; size = 0; } public boolean add(E e) { tail = (tail + 1) % capacity; elements[tail] = e; size = (size + 1) > capacity ? capacity : size + 1; head = (tail + 1 + capacity - size) % capacity; return true; } public E remove() { if (size == 0) return null; E element = (E) elements[head]; head = (head + 1) % capacity; size--; return element; } public E element() { if (size == 0) return null; E element = (E) elements[head]; return element; } public int size() { return size; } public boolean empty() { return size == 0; } public String toString() { StringBuilder sb = new StringBuilder(); sb.append('['); for (int i = 0, j = head; i < size; j = (j + 1) % capacity, i++) { if (i != 0) sb.append(','); sb.append(elements[j]); } sb.append(']'); return sb.toString(); } public static void main(String[] args) { FixedSizeQueue<Integer> queue = new FixedSizeQueue<Integer>(10); for (int i = 0; i < 35; i++) { queue.add(i); } System.out.println(queue); for (int i = 0; i < 5; i++) { System.out.println("remove " + queue.remove()); } System.out.println(queue); for (int i = 0; i < 7; i++) { queue.add(i); } System.out.println(queue); }}输出[25,26,27,28,29,30,31,32,33,34]remove 25remove 26remove 27remove 28remove 29[30,31,32,33,34][32,33,34,0,1,2,3,4,5,6] import java.lang.reflect.Array;import java.util.ArrayList;import java.util.Collection;import java.util.ConcurrentModificationException;import java.util.Iterator;import java.util.NoSuchElementException;import java.util.Queue;@SuppressWarnings("unchecked")public class FixedSizeQueue<E> implements Queue<E> { private Object[] elements; private int capacity; private int head; private int tail; private int size; private int modCount; public FixedSizeQueue(int capacity) { if (capacity < 0) throw new IllegalArgumentException("Illegal Capacity: " + capacity); elements = new Object[capacity]; this.capacity = capacity; head = 0; tail = (head - 1) % capacity; size = 0; } @Override public boolean add(E e) { modCount++; tail = (tail + 1) % capacity; elements[tail] = e; size = (size + 1) > capacity ? capacity : size + 1; head = (tail + 1 + capacity - size) % capacity; return true; } @Override public E element() { if (size == 0) throw new NoSuchElementException(); E element = (E) elements[head]; return element; } @Override public boolean offer(E e) { return add(e); } @Override public E peek() { if (size == 0) return null; E element = (E) elements[head]; return element; } @Override public E poll() { modCount++; if (size == 0) return null; E element = (E) elements[head]; head = (head + 1) % capacity; size--; return element; } @Override public E remove() { modCount++; if (size == 0) throw new NoSuchElementException(); ; E element = (E) elements[head]; head = (head + 1) % capacity; size--; return element; } @Override public boolean addAll(Collection<? extends E> c) { for (E e : c) { add(e); } return true; } @Override public void clear() { modCount++; size = 0; } @Override public boolean contains(Object o) { if (o == null) { for (Object obj : elements) { if (obj == null) { return true; } } } else { for (Object obj : elements) { if (o.equals(obj)) { return true; } } } return false; } @Override public boolean containsAll(Collection<?> c) { if (c.size() > size) { return false; } for (Object o : c) { if (!contains(o)) { return false; } } return true; } @Override public boolean isEmpty() { return size == 0; } @Override public Iterator<E> iterator() { return new Iter(); } @Override public boolean remove(Object o) { modCount++; if (o == null) { for (int i = 0, j = head; i < size; i++, j = (j + 1) % capacity) { Object obj = elements[j]; if (obj == null) { if (j >= head) { System.arraycopy(elements, head, elements, (head + 1) % capacity, i); head = (head + 1) % capacity; size--; } else { System.arraycopy(elements, j + 1, elements, j, size - i - 1); tail = (tail - 1) % capacity; size--; } return true; } } } else { for (int i = 0, j = head; i < size; i++, j = (j + 1) % capacity) { Object obj = elements[j]; if (o.equals(obj)) { if (j >= head) { System.arraycopy(elements, head, elements, (head + 1) % capacity, i); head = (head + 1) % capacity; size--; } else { System.arraycopy(elements, j + 1, elements, j, size - i - 1); tail = (tail - 1) % capacity; size--; } return true; } } } return false; } @Override public boolean removeAll(Collection<?> c) { int count = 0; Iterator<?> e = iterator(); while (e.hasNext()) { if (c.contains(e.next())) { e.remove(); count++; } } modCount += count; return count != 0; } @Override public boolean retainAll(Collection<?> c) { int count = 0; Iterator<?> e = iterator(); while (e.hasNext()) { if (!c.contains(e.next())) { e.remove(); count++; } } modCount += count; return count != 0; } @Override public int size() { return size; } @Override public Object[] toArray() { Object[] arr = new Object[size]; for (int i = 0, j = head; i < size; i++, j = (j + 1) % capacity) { arr[i] = elements[j]; } return arr; } @Override public <T> T[] toArray(T[] a) { if (a.length < size) { T[] arr = (T[]) Array.newInstance(a.getClass().getComponentType(), size); for (int i = 0, j = head; i < size; i++, j = (j + 1) % capacity) { arr[i] = (T) elements[j]; } return (T[]) arr; } for (int i = 0, j = head; i < size; i++, j = (j + 1) % capacity) { a[i] = (T) elements[j]; } if (a.length > size) { a[size] = null; } return a; } private class Iter implements Iterator<E> { int cursor = 0; int lastRet = -1; int expectedModCount = modCount; @Override public boolean hasNext() { return cursor != size(); } @Override public E next() { checkForComodification(); E next = (E) elements[(head + cursor) % capacity]; lastRet = cursor++; return next; } @Override public void remove() { if (lastRet == -1) throw new IllegalStateException(); checkForComodification(); int j = (head + lastRet) % capacity; if (j >= head) { System.arraycopy(elements, head, elements, (head + 1) % capacity, lastRet); head = (head + 1) % capacity; size--; } else { System.arraycopy(elements, j + 1, elements, j, size - lastRet - 1); tail = (tail - 1) % capacity; size--; } if (lastRet < cursor) cursor--; lastRet = -1; } final void checkForComodification() { if (modCount != expectedModCount) throw new ConcurrentModificationException(); } } public String toString() { StringBuilder sb = new StringBuilder(); sb.append('['); for (int i = 0, j = head; i < size; j = (j + 1) % capacity, i++) { if (i != 0) sb.append(',').append(' '); sb.append(elements[j]); } sb.append(']'); return sb.toString(); } public static void main(String[] args) { FixedSizeQueue<Integer> queue = new FixedSizeQueue<Integer>(10); for (int i = 0; i < 35; i++) { queue.add(i); } System.out.println(queue); ArrayList<Integer> list = new ArrayList<Integer>(); for (int i = 32; i < 35; i++) { list.add(i); } queue.retainAll(list); System.out.println(queue); System.out.println(queue.contains(31)); }}很十三的去implements Queue<E>……功能是都实现了,有没有bug不知道…… 异常处理throws、throw、try catch这三者的区别 java中的简单问题 如何设置 AWT 的 java.awt.Menu 的快捷键? 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Object[] elements;
int capacity;
int head;
int tail;
int size; public FixedSizeQueue(int capacity) {
if (capacity < 0)
throw new IllegalArgumentException("Illegal Capacity: " + capacity);
elements = new Object[capacity];
this.capacity = capacity;
head = 0;
tail = (head - 1) % capacity;
size = 0;
} public boolean add(E e) {
tail = (tail + 1) % capacity;
elements[tail] = e;
size = (size + 1) > capacity ? capacity : size + 1;
head = (tail + 1 + capacity - size) % capacity;
return true;
} public E remove() {
if (size == 0)
return null;
E element = (E) elements[head];
head = (head + 1) % capacity;
size--;
return element;
} public E element() {
if (size == 0)
return null;
E element = (E) elements[head];
return element;
} public int size() {
return size;
} public boolean empty() {
return size == 0;
} public String toString() {
StringBuilder sb = new StringBuilder();
sb.append('[');
for (int i = 0, j = head; i < size; j = (j + 1) % capacity, i++) {
if (i != 0)
sb.append(',');
sb.append(elements[j]);
}
sb.append(']');
return sb.toString();
} public static void main(String[] args) {
FixedSizeQueue<Integer> queue = new FixedSizeQueue<Integer>(10);
for (int i = 0; i < 35; i++) {
queue.add(i);
}
System.out.println(queue);
for (int i = 0; i < 5; i++) {
System.out.println("remove " + queue.remove());
}
System.out.println(queue);
for (int i = 0; i < 7; i++) {
queue.add(i);
}
System.out.println(queue);
}
}
输出
[25,26,27,28,29,30,31,32,33,34]
remove 25
remove 26
remove 27
remove 28
remove 29
[30,31,32,33,34]
[32,33,34,0,1,2,3,4,5,6]
import java.util.ArrayList;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Queue;@SuppressWarnings("unchecked")
public class FixedSizeQueue<E> implements Queue<E> {
private Object[] elements;
private int capacity;
private int head;
private int tail;
private int size; private int modCount; public FixedSizeQueue(int capacity) {
if (capacity < 0)
throw new IllegalArgumentException("Illegal Capacity: " + capacity);
elements = new Object[capacity];
this.capacity = capacity;
head = 0;
tail = (head - 1) % capacity;
size = 0;
} @Override
public boolean add(E e) {
modCount++;
tail = (tail + 1) % capacity;
elements[tail] = e;
size = (size + 1) > capacity ? capacity : size + 1;
head = (tail + 1 + capacity - size) % capacity;
return true;
} @Override
public E element() {
if (size == 0)
throw new NoSuchElementException();
E element = (E) elements[head];
return element;
} @Override
public boolean offer(E e) {
return add(e);
} @Override
public E peek() {
if (size == 0)
return null;
E element = (E) elements[head];
return element;
} @Override
public E poll() {
modCount++;
if (size == 0)
return null;
E element = (E) elements[head];
head = (head + 1) % capacity;
size--;
return element;
} @Override
public E remove() {
modCount++;
if (size == 0)
throw new NoSuchElementException();
;
E element = (E) elements[head];
head = (head + 1) % capacity;
size--;
return element;
} @Override
public boolean addAll(Collection<? extends E> c) {
for (E e : c) {
add(e);
}
return true;
} @Override
public void clear() {
modCount++;
size = 0;
} @Override
public boolean contains(Object o) {
if (o == null) {
for (Object obj : elements) {
if (obj == null) {
return true;
}
}
} else {
for (Object obj : elements) {
if (o.equals(obj)) {
return true;
}
}
}
return false;
} @Override
public boolean containsAll(Collection<?> c) {
if (c.size() > size) {
return false;
}
for (Object o : c) {
if (!contains(o)) {
return false;
}
}
return true;
} @Override
public boolean isEmpty() {
return size == 0;
} @Override
public Iterator<E> iterator() {
return new Iter();
} @Override
public boolean remove(Object o) {
modCount++;
if (o == null) {
for (int i = 0, j = head; i < size; i++, j = (j + 1) % capacity) {
Object obj = elements[j];
if (obj == null) {
if (j >= head) {
System.arraycopy(elements, head, elements, (head + 1)
% capacity, i);
head = (head + 1) % capacity;
size--;
} else {
System.arraycopy(elements, j + 1, elements, j, size - i
- 1);
tail = (tail - 1) % capacity;
size--;
}
return true;
}
}
} else {
for (int i = 0, j = head; i < size; i++, j = (j + 1) % capacity) {
Object obj = elements[j];
if (o.equals(obj)) {
if (j >= head) {
System.arraycopy(elements, head, elements, (head + 1)
% capacity, i);
head = (head + 1) % capacity;
size--;
} else {
System.arraycopy(elements, j + 1, elements, j, size - i
- 1);
tail = (tail - 1) % capacity;
size--;
}
return true;
}
}
}
return false;
} @Override
public boolean removeAll(Collection<?> c) {
int count = 0;
Iterator<?> e = iterator();
while (e.hasNext()) {
if (c.contains(e.next())) {
e.remove();
count++;
}
}
modCount += count;
return count != 0;
} @Override
public boolean retainAll(Collection<?> c) {
int count = 0;
Iterator<?> e = iterator();
while (e.hasNext()) {
if (!c.contains(e.next())) {
e.remove();
count++;
}
}
modCount += count;
return count != 0;
} @Override
public int size() {
return size;
} @Override
public Object[] toArray() {
Object[] arr = new Object[size];
for (int i = 0, j = head; i < size; i++, j = (j + 1) % capacity) {
arr[i] = elements[j];
}
return arr;
} @Override
public <T> T[] toArray(T[] a) {
if (a.length < size) {
T[] arr = (T[]) Array.newInstance(a.getClass().getComponentType(),
size);
for (int i = 0, j = head; i < size; i++, j = (j + 1) % capacity) {
arr[i] = (T) elements[j];
}
return (T[]) arr;
}
for (int i = 0, j = head; i < size; i++, j = (j + 1) % capacity) {
a[i] = (T) elements[j];
}
if (a.length > size) {
a[size] = null;
}
return a;
} private class Iter implements Iterator<E> {
int cursor = 0;
int lastRet = -1;
int expectedModCount = modCount; @Override
public boolean hasNext() {
return cursor != size();
} @Override
public E next() {
checkForComodification();
E next = (E) elements[(head + cursor) % capacity];
lastRet = cursor++;
return next;
} @Override
public void remove() {
if (lastRet == -1)
throw new IllegalStateException();
checkForComodification();
int j = (head + lastRet) % capacity;
if (j >= head) {
System.arraycopy(elements, head, elements, (head + 1)
% capacity, lastRet);
head = (head + 1) % capacity;
size--;
} else {
System.arraycopy(elements, j + 1, elements, j, size - lastRet
- 1);
tail = (tail - 1) % capacity;
size--;
}
if (lastRet < cursor)
cursor--;
lastRet = -1;
} final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
} } public String toString() {
StringBuilder sb = new StringBuilder();
sb.append('[');
for (int i = 0, j = head; i < size; j = (j + 1) % capacity, i++) {
if (i != 0)
sb.append(',').append(' ');
sb.append(elements[j]);
}
sb.append(']');
return sb.toString();
} public static void main(String[] args) {
FixedSizeQueue<Integer> queue = new FixedSizeQueue<Integer>(10);
for (int i = 0; i < 35; i++) {
queue.add(i);
}
System.out.println(queue);
ArrayList<Integer> list = new ArrayList<Integer>();
for (int i = 32; i < 35; i++) {
list.add(i);
}
queue.retainAll(list);
System.out.println(queue);
System.out.println(queue.contains(31));
}
}
很十三的去implements Queue<E>……
功能是都实现了,有没有bug不知道……