Java 中的 Deque offerFirst()方法

原文:https://www . geesforgeks . org/deque-offer first-method-in-Java/

offerFirst(E e) 方法的 德格接口 将指定的元素插入到德格的前面，如果有可能的话，在不违反容量限制的情况下立即插入。此方法优于 addFirst() 方法，因为此方法在容器容量满时不会抛出异常，因为它返回 false。

语法:

boolean offerFirst(E e)

参数:此方法接受一个强制参数 e ，它是要插入到德格前面的元素。

返回:该方法在成功插入时返回真，否则返回假。

异常:函数抛出四个异常，描述如下:

  • classcastexception : When the class of the element to be input prevents it from being added to this container.
  • [T0】 IllegalArgumentException 【T1]: When some attributes of an element prevent it from being added to Deque.
  • [T0】 NullPointerException 【T1]: When the element to be inserted is passed as null, and the interface of Deque does not allow null elements.

下面的程序说明了 offerFirst()的方法:

程序 1:

// Java Program Demonstrate offerFirst()
// method of Deque when Null is passed
import java.util.*;
import java.util.concurrent.LinkedBlockingDeque;

public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {

        // create object of Deque
        Deque<Integer> DQ
            = new LinkedBlockingDeque<Integer>(3);

        if (DQ.offerFirst(10))
            System.out.println("The Deque is not full and 10 is inserted");
        else
            System.out.println("The Deque is full");

        if (DQ.offerFirst(15))
            System.out.println("The Deque is not full and 15 is inserted");
        else
            System.out.println("The Deque is full");

        if (DQ.offerFirst(25))
            System.out.println("The Deque is not full and 25 is inserted");
        else
            System.out.println("The Deque is full");

        if (DQ.offerFirst(20))
            System.out.println("The Deque is not full and 20 is inserted");
        else
            System.out.println("The Deque is full");

        // before removing print Deque
        System.out.println("Deque: " + DQ);
    }
}

输出:

The Deque is not full and 10 is inserted
The Deque is not full and 15 is inserted
The Deque is not full and 25 is inserted
The Deque is full
Deque: [25, 15, 10]

节目 2:

// Java Program Demonstrate offerFirst()
// method of Queue when Null is passed
import java.util.*;
import java.util.concurrent.LinkedBlockingDeque;

public class GFG {
    public static void main(String[] args)
        throws NullPointerException
    {

        // create object of Queue
        Deque<Integer> DQ
            = new LinkedBlockingDeque<Integer>();

        // Add numbers to end of Deque
        DQ.offerFirst(7855642);
        DQ.offerFirst(35658786);
        DQ.offerFirst(5278367);

        // when null is inserted
        DQ.offerFirst(null);

        // before removing print Deque
        System.out.println("Deque: " + DQ);
    }
}

输出:

Exception in thread "main" java.lang.NullPointerException
    at java.util.concurrent.LinkedBlockingDeque.offerFirst(LinkedBlockingDeque.java:342)
    at GFG.main(GFG.java:21)

注意:另外两个异常是内部异常，是由编译器导致的，因此不能在代码中显示。

参考:https://docs . Oracle . com/javae/8/docs/API/Java/util/deue . html # offeroforerst-e-

版权属于：月萌API www.moonapi.com，转载请注明出处

本文链接：https://www.moonapi.com/news/19904.html