How do you avoid an ArrayList object from being modified, i.e. avoid adding and deleting its content

[Anjali Lamba]

How do you avoid an ArrayList object from being modified, i.e. avoid adding and deleting its content

[Campbell Ritchie]

Go through the java.util.Collections class, where you will find methods allowing you to make a read-only copy of Lists, etc.

[Javin Paul]

Use following methods:

unmodifiableSet -- for getting unmodifiable version of Set
unmodifiableMap
unmodifiableList

etc.

[vinayak jog]

ArrayList al = new ArrayList();
al.add("string");

al =(ArrayList)Collections.unmodifiableCollection(al);

[Harsha Smith]

vinayak jog wrote: ArrayList al = new ArrayList();
al.add("string");

al =(ArrayList)Collections.unmodifiableCollection(al);

wrong answer. throws class cast exception

[vinayak jog]

Harsha Smith wrote:

vinayak jog wrote: ArrayList al = new ArrayList();
al.add("string");

al =(ArrayList)Collections.unmodifiableCollection(al);

wrong answer. throws class cast exception

List<String> al = new ArrayList<String>();
al.add("hello world");

al =(List)Collections.unmodifiableList(al);
System.out.println(al.get(0));

[Ernest Friedman-Hill]

vinayak jog wrote:

    List<String> al = new ArrayList<String>();
    al.add("hello world");
    al =(List)Collections.unmodifiableList(al);
    System.out.println(al.get(0));

Better -- although the cast at line 3 is redundant.

[Rob Spoor]

Campbell Ritchie wrote:Go through the java.util.Collections class, where you will find methods allowing you to make a read-only copy of Lists, etc.

Not a copy - a view. A copy implies that the data is copied and that modifying the original will not affect the copy. A view implies that the data is not copied and changes in the original will be seen in the view.

[Campbell Ritchie]

Good point, Rob. One needs to be precise.
Note that the unmodifiable method returns a view, but the original List is still usually extant, and that can be modified.