think in java容器深入研究（未擷取支援的操作）

分析一個簡單的代碼

package containers;//: containers/Unsupported.java// Unsupported operations in Java containers.import java.util.*;public class Unsupported {  static void test(String msg, List<String> list) {    System.out.println("--- " + msg + " ---");    Collection<String> c = list;    Collection<String> subList = list.subList(1,8);    // Copy of the sublist:    Collection<String> c2 = new ArrayList<String>(subList);    try { c.retainAll(c2); } catch(Exception e) {      System.out.println("retainAll(): " + e);    }    try { c.removeAll(c2); } catch(Exception e) {      System.out.println("removeAll(): " + e);    }    try { c.clear(); } catch(Exception e) {      System.out.println("clear(): " + e);    }    try { c.add("X"); } catch(Exception e) {      System.out.println("add(): " + e);    }    try { c.addAll(c2); } catch(Exception e) {      System.out.println("addAll(): " + e);    }    try { c.remove("C"); } catch(Exception e) {      System.out.println("remove(): " + e);    }  }  public static void main(String[] args) {    List<String> list =      Arrays.asList("A B C D E F G H I J K L".split(" "));    test("Modifiable Copy", new ArrayList<String>(list));    test("Arrays.asList()", list);  }} /* Output:--- Modifiable Copy ------ Arrays.asList() ---retainAll(): java.lang.UnsupportedOperationExceptionremoveAll(): java.lang.UnsupportedOperationExceptionclear(): java.lang.UnsupportedOperationExceptionadd(): java.lang.UnsupportedOperationExceptionaddAll(): java.lang.UnsupportedOperationExceptionremove(): java.lang.UnsupportedOperationException*///:~

在main方法中test("Modifiable Copy", new ArrayList<String>(list));這行代碼執行沒有任何問題。

test("Arrays.asList()", list);代碼在執行後，拋出了一堆的異常"java.lang.UnsupportedOperationException”。

 

分析結果：

List<String> list = Arrays.asList("A B C D E F G H I J K L".split(" "));

這行代碼通過Arrays.asList產生Stirng[]數組，數組固定的長度，不允許對數組進行增加、刪除、等操作。

這行代碼test("Modifiable Copy", new ArrayList<String>(list));，將產生的數組，採用ArrayList容器進行封裝，經查詢源碼ArrayList類繼承AbstractList並實現List介面，並可以進行增加、刪除、等操作。

public class ArrayList extends AbstractList        implements List, RandomAccess, Cloneable, java.io.Serializable

查看AbstractList源碼會發現，如果單單繼承AbstractList但未重寫add方法，則會拋出UnsupportedOperationException異常。

public abstract class AbstractList extends AbstractCollection implements List {    /**     * Sole constructor.  (For invocation by subclass constructors, typically     * implicit.)     */    protected AbstractList() {    }    public void add(int index, Object element) {throw new UnsupportedOperationException();    }