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Java Deque addFirst()用法及代碼示例


如果有空間，則Deque接口的addFirst(E e)方法會將參數中傳遞的元素插入到Deque的前麵。如果Deque受容量限製並且沒有剩餘空間可插入，則它將返回IllegalStateException。成功插入後，該函數返回true。

用法:

void addFirst(E e)

參數：此方法接受強製性參數e，該參數是要插入到雙端隊列的前麵的元素。

返回：成功插入後，此方法返回true。

異常：該函數引發四個異常，如下所述：



  • ClassCastException：當要輸入的元素的類阻止將其添加到此容器中時：
  • IllegalStateException：當容器的容量已滿並且已插入時。
  • IllegalArgumentException：當元素的某些屬性阻止將其添加到雙端隊列時。
  • NullPointerException ：當要插入的元素作為null傳遞並且Deque的接口不允許使用null元素時：

以下示例程序旨在說明Deque的addFirst()方法：

程序1:借助LinkedList。

// Java Program Demonstrate addFirst() 
// method of Deque 
import java.util.*; 
  
public class GFG { 
    public static void main(String[] args) 
        throws IllegalStateException 
    { 
  
        // create object of De1ue 
        Deque<Integer> DQ 
            = new LinkedList<Integer>(); 
  
        // Add numbers to end of Deque 
        DQ.addFirst(7855642); 
        DQ.addFirst(35658786); 
        DQ.addFirst(5278367); 
        DQ.addFirst(74381793); 
  
        // print Deque 
        System.out.println("Deque:" + DQ); 
    } 
}
輸出： 
Deque:[74381793, 5278367, 35658786, 7855642]

程序2:借助ArrayDeque。

// Java Program Demonstrate addFirst() 
// method of Deque 
import java.util.*; 
  
public class GFG { 
    public static void main(String[] args) 
        throws IllegalStateException 
    { 
  
        // create object of De1ue 
        Deque<Integer> DQ 
            = new ArrayDeque<Integer>(); 
  
        // Add numbers to end of Deque 
        DQ.addFirst(7855642); 
        DQ.addFirst(35658786); 
        DQ.addFirst(5278367); 
        DQ.addFirst(74381793); 
  
        // print Deque 
        System.out.println("Deque:" + DQ); 
    } 
}
輸出： 
Deque:[74381793, 5278367, 35658786, 7855642]

程序3:借助ConcurrentLinkedDeque。

// Java Program Demonstrate addFirst() 
// method of Deque 
import java.util.*; 
import java.util.concurrent.ConcurrentLinkedDeque; 
public class GFG { 
    public static void main(String[] args) 
        throws IllegalStateException 
    { 
  
        // create object of De1ue 
        Deque<Integer> DQ 
            = new ConcurrentLinkedDeque<Integer>(); 
  
        // Add numbers to end of Deque 
        DQ.addFirst(7855642); 
        DQ.addFirst(35658786); 
        DQ.addFirst(5278367); 
        DQ.addFirst(74381793); 
  
        // print Deque 
        System.out.println("Deque:" + DQ); 
    } 
}
輸出： 
Deque:[74381793, 5278367, 35658786, 7855642]

程序4:借助LinkedBlockingDeque。



// Java Program Demonstrate addFirst() 
// method of Deque 
import java.util.*; 
import java.util.concurrent.LinkedBlockingDeque; 
public class GFG { 
    public static void main(String[] args) 
        throws IllegalStateException 
    { 
  
        // create object of De1ue 
        Deque<Integer> DQ 
            = new LinkedBlockingDeque<Integer>(); 
  
        // Add numbers to end of Deque 
        DQ.addFirst(7855642); 
        DQ.addFirst(35658786); 
        DQ.addFirst(5278367); 
        DQ.addFirst(74381793); 
  
        // print Deque 
        System.out.println("Deque:" + DQ); 
    } 
}
輸出： 
Deque:[74381793, 5278367, 35658786, 7855642]

以下示例程序旨在說明addFirst()方法引發的異常：

程序5:顯示NullPointerException。

/// Java Program Demonstrate addFirst() 
// 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>(); 
  
        // Add numbers to end of DeQue 
        DQ.addFirst(7855642); 
        DQ.addFirst(35658786); 
        DQ.addFirst(5278367); 
        // when null is inserted 
        DQ.addFirst(null); 
  
        // before removing print DeQue 
        System.out.println("DeQue:" + DQ); 
    } 
}

輸出：

Exception in thread "main" java.lang.NullPointerException
    at java.util.concurrent.LinkedBlockingDeque.offerFirst(LinkedBlockingDeque.java:342)
    at java.util.concurrent.LinkedBlockingDeque.addFirst(LinkedBlockingDeque.java:325)
    at GFG.main(GFG.java:20)

程序6:顯示IllegalStateException。

// Java Program Demonstrate addFirst() 
// method of Deque when capacity is full 
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); 
  
        // Add numbers to end of Deque 
        DQ.addFirst(7855642); 
        DQ.addFirst(35658786); 
        DQ.addFirst(5278367); 
  
        // when capacity is full 
        DQ.addFirst(10); 
  
        // before removing print Deque 
        System.out.println("Deque:" + DQ); 
    } 
}

輸出：

Exception in thread "main" java.lang.IllegalStateException:Deque full
    at java.util.concurrent.LinkedBlockingDeque.addFirst(LinkedBlockingDeque.java:326)
    at GFG.main(GFG.java:21)

注意：其他兩個異常是內部的，它們是由編譯器引起的，因此無法在編譯器中顯示。

參考： https://docs.oracle.com/javase/8/docs/api/java/util/Deque.html#addFirst-E-

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注：本文由純淨天空篩選整理自gopaldave大神的英文原創作品 Deque addFirst() method in Java with Examples。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。