Java并将List的addAll方法使用<Character>

Question

I have something simple, but can't solve. I just want to add one list of chars to another . It's working with String types. Why does it not work with char ?

Character [] myChar={'a', 's', 'd','f', 't', 'i'};
List<Character> listChar= Arrays.asList(myChar);
Character[] newChar= new Character[listChar.size()];
List<Character> newlistChar= Arrays.asList(newChar);
Collections.fill(newlistChar, 'd');
output(newlistChar,"filled d");
Collections.addAll(listChar,newlistChar); // does not work

I tried to do something like casting the list, but still got an exception.

   ...((String)(listChar),(String)(newlistChar))

Even if I use something like this it still throws and exception. So how do I use addAll with char ?

Collections.addAll(listChar,newlistChar.toArray(new Character[newlistChar.size()]));

Answer 1

Unless this is [homework] , you should use a StringBuilder or just plain String.

// Using String
String myChars = "asdfti";
char[] ds = new char[mychars.length()];
Arrays.fill(ds, 'd');
myChars += new String(ds);

Answer 2

• asList returns a fixed size list, you can't add elements to it.
• Collections.addAll doesn't accept list as 2nd parameter

Use next:

    Character[] myChar = {'a', 's', 'd', 'f', 't', 'i'};
    List<Character> listChar = new ArrayList<Character>(Arrays.asList(myChar));
    Character[] newChar = new Character[listChar.size()];
    Arrays.fill(newChar, 'd');
    Collections.addAll(listChar, newChar);

Answer 3

List returned from Arrays.asList has fixed size. You cannot add anything to it.

Instead, add both lists to new ArrayList .

Answer 4

Have you read the javadoc of Collections.addAll() ?

Its signature is

public static <T> boolean addAll(Collection<? super T> c,
                                 T... elements)

This means that the second argument is a varargs. You may thus pass an array of Characters, or individual Character instances:

Collections.addAll(listChar, new Character[] {'a', 'b'});
Collections.addAll(listChar, Character.valueOf('a'), Character.valueOf('b'));

But a List<Character> is an invalid type for the second argument.

A good way to know is to actually read the compiler error message. Usually, they're much more informative than "it doesn't work".

And another problem is that the lists returned by Arrays.asList() have a fixed size. You can't add anything to them.

Answer 5

Would this code snippet help?

    ArrayList<Character> myChar = new ArrayList<Character>();
    myChar.add('a');
    myChar.add('s'); 
    myChar.add('d');
    myChar.add('f'); 
    myChar.add('t'); 
    myChar.add('i');

    ArrayList<Character> newlistChar= new ArrayList<Character>();
    newlistChar.add('d');

    myChar.addAll(newlistChar);

Answer 6

change the last line to

Collections.addAll(listChar, newlistChar.toArray(new Character[newlistChar.size()]));