Thinking in Java 4 學習筆記

P220 主題：在測試Arrays.asList()發現的問題

@SafeVarargs
    public static 
   
     List
    
      asList(T... a) {
        return new ArrayList<>(a);
    }
    
   
           

以上是eclipse反編譯的代碼片段；

直接複制使用編譯不通過；

于是這樣:

import java.util.*;

public class ArrayTest
   
     {
	@SafeVarargs
    public static 
    
      List
     
       asList(Collection
      
        a) {
        return new ArrayList
       
        (a); } } import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class Test { public static void main(String[] args) { List
        
          k=new ArrayList
         
          (); System.out.println(ArrayTest.asList(k) instanceof ArrayList); System.out.println(Arrays.asList(k) instanceof ArrayList); int[] nums=new int[]{1,2,3}; System.out.println(Arrays.asList(nums) instanceof ArrayList); } } ---------console------- true false false 
         
        
       
      
     
    
   
           

覺得無法了解。。。求大神解釋！！

解答。。。asList中使用的是Arrays中的private 靜态内部類 ArrayList 以下是該内部類源碼。。注意：無add與delete方法

private static class ArrayList
   
     extends AbstractList
    
     
        implements RandomAccess, java.io.Serializable
    {
        private static final long serialVersionUID = -2764017481108945198L;
        private final E[] a;

        ArrayList(E[] array) {
            if (array==null)
                throw new NullPointerException();
            a = array;
        }

        public int size() {
            return a.length;
        }

        public Object[] toArray() {
            return a.clone();
        }

        public 
     
       T[] toArray(T[] a) {
            int size = size();
            if (a.length < size)
                return Arrays.copyOf(this.a, size,
                                     (Class
      ) a.getClass());
            System.arraycopy(this.a, 0, a, 0, size);
            if (a.length > size)
                a[size] = null;
            return a;
        }

        public E get(int index) {
            return a[index];
        }

        public E set(int index, E element) {
            E oldValue = a[index];
            a[index] = element;
            return oldValue;
        }

        public int indexOf(Object o) {
            if (o==null) {
                for (int i=0; i