Using Java 8 lambda:
ArrayList<Object> obj = new ArrayList<>();
obj.add(1);
obj.add("Java");
obj.add(3.14);
ArrayList<String> list = new ArrayList<>();
obj.forEach((xx) -> list.add(String.valueOf(xx)));
A simple solution:
List<Object> lst =listOfTypeObject;
ArrayList<String> aryLst = new ArrayList<String>();
for (int i = 0; i < lst.size(); i++) {
aryLst.add(lst.get(i).toString());
}
Note: this works when the list contains all the elements of datatype String.
Here is another alternative using Guava
List<Object> lst ...
List<String> ls = Lists.transform(lst, Functions.toStringFunction());
Using Java 8 you can do:
List<Object> list = ...;
List<String> strList = list.stream()
.map( Object::toString )
.collect( Collectors.toList() );
With Java Generics Takes a list of X and returns a list of T that extends or implements X, Sweet!
// the cast is is actually checked via the method API
@SuppressWarnings("unchecked")
public static <T extends X, X> ArrayList<T> convertToClazz(ArrayList<X> from, Class<X> inClazz, Class<T> outClazz) {
ArrayList<T> to = new ArrayList<T>();
for (X data : from) {
to.add((T) data);
}
return to;
}
You can use wildcard to do this as following
ArrayList<String> strList = (ArrayList<String>)(ArrayList<?>)(list);
It's not safe to do that!
Imagine if you had:
ArrayList<Object> list = new ArrayList<Object>();
list.add(new Employee("Jonh"));
list.add(new Car("BMW","M3"));
list.add(new Chocolate("Twix"));
It wouldn't make sense to convert the list of those Objects to any type.
Your code ArrayList<String> list2 = (String)list;
does not compile because list2
is not of type String
. But that is not the only problem.
Using guava:
List<String> stringList=Lists.transform(list,new Function<Object,String>(){
@Override
public String apply(Object arg0) {
if(arg0!=null)
return arg0.toString();
else
return "null";
}
});
If you want to do it the dirty way, try this.
@SuppressWarnings("unchecked")
public ArrayList<String> convert(ArrayList<Object> a) {
return (ArrayList) a;
}
Advantage: here you save time by not iterating over all objects.
Disadvantage: may produce a hole in your foot.
Source: Stackoverflow.com