Java 为什么 ArrayList 类的 removeRange 方法不起作用？
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Why removeRange method of ArrayList class is not working?
提问by Chaitanya
I am trying to use removeRangemethod for removing certain elements from ArrayList. I got to know about this method from here: http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#removeRange(int, int)
我正在尝试使用removeRange方法从ArrayList. 我从这里了解了这种方法：http: //docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#removeRange(int, int)
However when I tried it like this
但是当我像这样尝试时
ArrayList<String> al = new ArrayList<String>();
al.add("AB");
al.add("BC");
al.add("CD");
al.add("DE");
al.removeRange(1, 3);
I got this error:
我收到此错误：
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
The method removeRange(int, int) from the type ArrayList<String> is not visible
Why am I not able to use this method? Am I doing something wrong?
为什么我不能使用这种方法？难道我做错了什么？
采纳答案by Suresh Atta
Since it a protected method , it is visible to only class ,package and subclasses.
因为它是一个受保护的方法，所以它只对类、包和子类可见。
The protected modifier specifies that the member can only be accessed within its own package (as with package-private) and, in addition, by a subclass of its class in another package.
protected 修饰符指定该成员只能在它自己的包内访问（如包私有），此外，它的类的子类在另一个包中可以访问。
Modifier Class Package Subclass World
---------------------------------------------
public Y Y Y Y
protected Y Y Y N
no modifier Y Y N N
private Y N N N
http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html
http://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html
回答by René Link
The short answer is: Use
简短的回答是：使用
al.subList(1, 3).clear();
The removeRange(int, int)method is protected. You can only invoke it from a subclass of ArrayListor from a class within the same package as ArrayList. See Controlling Access to Members of a Class.
该removeRange(int, int)方法protected。您只能从ArrayList与ArrayList. 请参阅控制对类成员的访问。
The only way to access the removeRangemethod is to subclass ArrayListand make the method public. E.g.
访问该removeRange方法的唯一方法是子类化ArrayList并公开该方法。例如
public class RangeRemoveSupport<E> extends ArrayList<E> {
public void removeRange(int fromIndex, int toIndex) {
super.removeRange(fromIndex, toIndex);
}
}
But then your code must use the subclass. Thus your code depends on this subclass and not just depends on Listor ArrayList.
但是你的代码必须使用子类。因此，您的代码取决于此子类，而不仅仅是取决于Listor ArrayList。
A utility class within the same package to access it is not possible. E.g.
同一个包中的实用程序类无法访问它。例如
package java.util; // <- SecurityException
public class RemoveRangeSupport {
public static void removeRange(ArrayList<?> list, int from, int to){
list.removeRange(from, to);
}
}
This will cause a SecurityException
这将导致一个 SecurityException
java.lang.SecurityException: Prohibited package name: java.util.
java.lang.SecurityException: Prohibited package name: java.util.
because you are not allowed to define classes in java.utilfor security reasons.
因为java.util出于安全原因，您不允许定义类。
Nevertheless for other packages it might be a way.
不过对于其他包，这可能是一种方式。
I often use this strategy for tests. Then I put such a utility class in the same package as the production code to access some internals from tests that should normally not be accessible. This is an easy way without using a framework.
我经常使用这种策略进行测试。然后我将这样一个实用程序类与生产代码放在同一个包中，以便从通常无法访问的测试中访问一些内部组件。这是一种无需使用框架的简单方法。
EDIT
编辑
Is there perhaps a function to replace items from range X..Y, to new items of a possible different size?
for example: this list "0,1,2,3,4", I replace from 1..3 with "a,b,c,d,e", will result with : "0,a,b,c,d,e,4".
是否有一个功能可以将范围 X..Y 中的项目替换为可能不同大小的新项目？
例如：这个列表“0,1,2,3,4”，我从 1..3 替换为“a,b,c,d,e”，结果为：“0,a,b,c, d,e,4"。
List<String> list = new ArrayList<>(Arrays.asList("0", "1", "2", "3", "4"));
List<String> subList = list.subList(1, 4);
subList.clear();
subList.addAll(Arrays.asList("a", "b", "c", "d", "e"));
System.out.println(list);
will output
会输出
[0, a, b, c, d, e, 4]
回答by Aroon
You can use: a1.subList(1, 3).clear(); It has already been discussed here:Why is Java's AbstractList's removeRange() method protected?It might help you to understand better.
您可以使用： a1.subList(1, 3).clear(); 这里已经讨论过：为什么 Java 的 AbstractList 的 removeRange() 方法受到保护？它可能会帮助您更好地理解。
回答by Ruben Vardanyan
removeRange(int firstIndex, int lastIndex)method is protectedmethod in ArrayList<Object>. Protected method is accessed in class, subclasses and in package, but not public.
removeRange(int firstIndex, int lastIndex)方法是 中的protected方法ArrayList<Object>。受保护的方法可以在类、子类和包中访问，但不是公共的。
