Java中的队列 offer() 方法
队列接口的offer(E e)方法在不违反容量限制的情况下立即将指定元素插入此队列。此方法优于add()方法，因为此方法在容器容量已满时不会抛出异常，因为它返回 false。
句法：
boolean offer(E e)参数：此方法接受一个强制参数e ，它是要插入到队列中的元素。
返回：此方法在成功插入时返回 true，否则返回 false。
异常：该函数抛出四个异常，描述如下：
- ClassCastException ：当要输入的元素的类阻止它被添加到这个容器时。
- IllegalArgumentException ：当元素的某些属性阻止将其添加到队列中时。
- NullPointerException : 当要插入的元素作为 null 传递并且队列的接口不允许 null 元素时。
下面的程序说明了 Queue 的 offer() 方法：
程序 1：在LinkedBlockingDeque的帮助下。
// Java Program Demonstrate offer()
// method of Queue
import java.util.*;
import java.util.concurrent.LinkedBlockingQueue;
public class GFG {
public static void main(String[] args)
throws IllegalStateException
{
// create object of Queue
Queue Q
= new LinkedBlockingQueue(3);
if (Q.offer(10))
System.out.println("The Queue is not full"
+ " and 10 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(15))
System.out.println("The Queue is not full"
+ " and 15 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(25))
System.out.println("The Queue is not full"
+ " and 25 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(20))
System.out.println("The Queue is not full"
+ " and 20 is inserted");
else
System.out.println("The Queue is full");
// before removing print Queue
System.out.println("Queue: " + Q);
}
}
输出：
The Queue is not full and 10 is inserted
The Queue is not full and 15 is inserted
The Queue is not full and 25 is inserted
The Queue is full
Queue: [10, 15, 25]
程序 2：在ConcurrentLinkedDeque的帮助下。
// Java Program Demonstrate offer()
// method of Queue
import java.util.*;
import java.util.concurrent.ConcurrentLinkedDeque;
public class GFG {
public static void main(String[] args)
throws IllegalStateException
{
// create object of Queue
Queue Q
= new ConcurrentLinkedDeque();
if (Q.offer(10))
System.out.println("The Queue is not full"
+ " and 10 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(15))
System.out.println("The Queue is not full"
+ " and 15 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(25))
System.out.println("The Queue is not full"
+ " and 25 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(20))
System.out.println("The Queue is not full"
+ " and 20 is inserted");
else
System.out.println("The Queue is full");
// before removing print Queue
System.out.println("Queue: " + Q);
}
}
输出：
The Queue is not full and 10 is inserted
The Queue is not full and 15 is inserted
The Queue is not full and 25 is inserted
The Queue is not full and 20 is inserted
Queue: [10, 15, 25, 20]
程序 3：在ArrayDeque的帮助下。
// Java Program Demonstrate offer()
// method of Queue
import java.util.*;
public class GFG {
public static void main(String[] args)
throws IllegalStateException
{
// create object of Queue
Queue Q
= new ArrayDeque(6);
if (Q.offer(10))
System.out.println("The Queue is not full"
+ " and 10 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(15))
System.out.println("The Queue is not full"
+ " and 15 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(25))
System.out.println("The Queue is not full"
+ " and 25 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(20))
System.out.println("The Queue is not full"
+ " and 20 is inserted");
else
System.out.println("The Queue is full");
// before removing print Queue
System.out.println("Queue: " + Q);
}
}
输出：
The Queue is not full and 10 is inserted
The Queue is not full and 15 is inserted
The Queue is not full and 25 is inserted
The Queue is not full and 20 is inserted
Queue: [10, 15, 25, 20]
程序 4：在LinkedList的帮助下。
// Java Program Demonstrate offer()
// method of Queue
import java.util.*;
public class GFG {
public static void main(String[] args)
throws IllegalStateException
{
// create object of Queue
Queue Q
= new LinkedList();
if (Q.offer(10))
System.out.println("The Queue is not full"
+ " and 10 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(15))
System.out.println("The Queue is not full"
+ " and 15 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(25))
System.out.println("The Queue is not full"
+ " and 25 is inserted");
else
System.out.println("The Queue is full");
if (Q.offer(20))
System.out.println("The Queue is not full"
+ " and 20 is inserted");
else
System.out.println("The Queue is full");
// before removing print Queue
System.out.println("Queue: " + Q);
}
}
输出：
The Queue is not full and 10 is inserted
The Queue is not full and 15 is inserted
The Queue is not full and 25 is inserted
The Queue is not full and 20 is inserted
Queue: [10, 15, 25, 20]
下面的程序说明了此方法引发的异常：
程序 5：显示NullPointerException 。
// Java Program Demonstrate offer()
// method of Queue when Null is passed
import java.util.*;
import java.util.concurrent.LinkedBlockingQueue;
public class GFG {
public static void main(String[] args)
throws NullPointerException
{
// create object of Queue
Queue Q
= new LinkedBlockingQueue();
// Add numbers to end of Deque
Q.offer(7855642);
Q.offer(35658786);
Q.offer(5278367);
try {
// when null is inserted
Q.offer(null);
}
catch (Exception e) {
System.out.println("Exception: " + e);
}
}
}
输出：
Exception: java.lang.NullPointerException
注意：其他两个异常是内部异常，由编译器引起，因此无法在代码中显示。
参考： https: Java/util/Queue.html#offer-E-