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Java AbstractSequentialList toArray(T[])用法及代码示例


Java中AbstractSequentialList类的toArray(arr [])方法方法用于生成与AbstractSequentialList相同元素的数组。它以正确的顺序返回一个数组,其中包含此AbstractSequentialList中的所有元素。返回数组的运行时类型是指定数组的运行时类型。如果AbstractSequentialList适合指定的数组,则在其中返回它。否则,将使用指定数组的运行时类型和此AbstractSequentialList的大小分配一个新数组。如果AbstractSequentialList适合指定的数组并有剩余空间(即,数组中的元素比AbstractSequentialList多),则将紧接AbstractSequentialList末尾的数组中的元素设置为null。 (仅当调用者知道AbstractSequentialList不包含任何null元素时,这才对确定AbstractSequentialList的长度很有用。)

用法:

public <T> T[] toArray(T[] a)

参数:该方法接受一个参数arr [](如果该参数足够大),该参数是将AbstractSequentialList的元素存储到的数组;否则,将为此分配一个具有相同运行时类型的新数组。


返回值:该方法返回一个包含与AbstractSequentialList相似的元素的数组。

异常:该方法可能会引发两种类型的异常:

  • ArrayStoreException:当提到的数组具有不同的类型并且无法与AbstractSequentialList中提到的元素进行比较时:
  • NullPointerException :如果数组为Null,则抛出此异常。

下面的程序演示了AbstractSequentialList.toArray(arr [])方法的用法。

程序1:当数组的大小为AbstractSequentialList时

// Java code to illustrate toArray(arr[]) 
  
import java.util.*; 
  
public class AbstractSequentialListDemo { 
    public static void main(String args[]) 
    { 
        // Creating an empty AbstractSequentialList 
        AbstractSequentialList<String> 
            abs_col = new LinkedList<String>(); 
  
        // Use add() method to add 
        // elements into the AbstractSequentialList 
        abs_col.add("Welcome"); 
        abs_col.add("To"); 
        abs_col.add("Geeks"); 
        abs_col.add("For"); 
        abs_col.add("Geeks"); 
  
        // Displaying the AbstractSequentialList 
        System.out.println("The AbstractSequentialList:"
                           + abs_col); 
  
        // Creating the array and using toArray() 
        String[] arr = new String[5]; 
        arr = abs_col.toArray(arr); 
  
        // Displaying arr 
        System.out.println("The arr[] is:"); 
        for (int j = 0; j < arr.length; j++) 
            System.out.println(arr[j]); 
    } 
}
输出:
The AbstractSequentialList:[Welcome, To, Geeks, For, Geeks]
The arr[] is:
Welcome
To
Geeks
For
Geeks

程序2:当数组小于AbstractSequentialList的大小时

// Java code to illustrate toArray(arr[]) 
  
import java.util.*; 
  
public class AbstractSequentialListDemo { 
    public static void main(String args[]) 
    { 
        // Creating an empty AbstractSequentialList 
        AbstractSequentialList<String> 
            abs_col = new LinkedList<String>(); 
  
        // Use add() method to add 
        // elements into the AbstractSequentialList 
        abs_col.add("Welcome"); 
        abs_col.add("To"); 
        abs_col.add("Geeks"); 
        abs_col.add("For"); 
        abs_col.add("Geeks"); 
  
        // Displaying the AbstractSequentialList 
        System.out.println("The AbstractSequentialList:"
                           + abs_col); 
  
        // Creating the array and using toArray() 
        String[] arr = new String[1]; 
        arr = abs_col.toArray(arr); 
  
        // Displaying arr 
        System.out.println("The arr[] is:"); 
        for (int j = 0; j < arr.length; j++) 
            System.out.println(arr[j]); 
    } 
}
输出:
The AbstractSequentialList:[Welcome, To, Geeks, For, Geeks]
The arr[] is:
Welcome
To
Geeks
For
Geeks

程序3:当数组大于AbstractSequentialList的大小时

// Java code to illustrate toArray(arr[]) 
  
import java.util.*; 
  
public class AbstractSequentialListDemo { 
    public static void main(String args[]) 
    { 
        // Creating an empty AbstractSequentialList 
        AbstractSequentialList<String> 
            abs_col = new LinkedList<String>(); 
  
        // Use add() method to add 
        // elements into the AbstractSequentialList 
        abs_col.add("Welcome"); 
        abs_col.add("To"); 
        abs_col.add("Geeks"); 
        abs_col.add("For"); 
        abs_col.add("Geeks"); 
  
        // Displaying the AbstractSequentialList 
        System.out.println("The AbstractSequentialList:"
                           + abs_col); 
  
        // Creating the array and using toArray() 
        String[] arr = new String[10]; 
        arr = abs_col.toArray(arr); 
  
        // Displaying arr 
        System.out.println("The arr[] is:"); 
        for (int j = 0; j < arr.length; j++) 
            System.out.println(arr[j]); 
    } 
}
输出:
The AbstractSequentialList:[Welcome, To, Geeks, For, Geeks]
The arr[] is:
Welcome
To
Geeks
For
Geeks
null
null
null
null
null

程序4:演示NullPointerException

// Java code to illustrate toArray(arr[]) 
  
import java.util.*; 
  
public class AbstractSequentialListDemo { 
    public static void main(String args[]) 
    { 
        // Creating an empty AbstractSequentialList 
        AbstractSequentialList<String> 
            abs_col = new LinkedList<String>(); 
  
        // Use add() method to add 
        // elements into the AbstractSequentialList 
        abs_col.add("Welcome"); 
        abs_col.add("To"); 
        abs_col.add("Geeks"); 
        abs_col.add("For"); 
        abs_col.add("Geeks"); 
  
        // Displaying the AbstractSequentialList 
        System.out.println("The AbstractSequentialList:"
                           + abs_col); 
  
        try { 
            // Creating the array 
            String[] arr = null; 
            // using toArray() 
            // Since arr is null 
            // Hence exception will be thrown 
            arr = abs_col.toArray(arr); 
  
            // Displaying arr 
            System.out.println("The arr[] is:"); 
            for (int j = 0; j < arr.length; j++) 
                System.out.println(arr[j]); 
        } 
        catch (Exception e) { 
            System.out.println("Exception:" + e); 
        } 
    } 
}
输出:
The AbstractSequentialList:[Welcome, To, Geeks, For, Geeks]
Exception:java.lang.NullPointerException


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注:本文由纯净天空筛选整理自Code_r大神的英文原创作品 AbstractSequentialList toArray(T[]) method in Java with Example。非经特殊声明,原始代码版权归原作者所有,本译文未经允许或授权,请勿转载或复制。