小弟我学习java是在codygym上练习的,我理解的Collections.addAll(list,array)方法可以把array添加到arraylist上,我这样理解是对的吗。
问题是在我做题的时候碰到这个:
package com.codegym.task.task10.task1012;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Collections;
/*
Number of letters
*/
public class Solution {
public static void main(String[] args) throws Exception {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
// Alphabet
String abc = "abcdefghijklmnopqrstuvwxyz";
char[] abcArray = abc.toCharArray();
ArrayList<Character> alphabet = new ArrayList<>();
for (char letter : abcArray) {
alphabet.add(letter);
}
// Read in strings
ArrayList<String> list = new ArrayList<>();
for (int i = 0; i < 10; i++) {
String s = reader.readLine();
list.add(s.toLowerCase());
}
// write your code here
HashMap<Character, Integer> alphaMap = new HashMap<Character, Integer>();
for (int i = 0; i < alphabet.size(); i++) {
alphaMap.put(alphabet.get(i), 0);
}
ArrayList<Character> wordsCharacter = new ArrayList<Character>();
//wordsCharacter.add('s');
for(int i = 0; i < list.size(); i++) {
Collections.addAll(wordsCharacter, list.get(i).toCharArray());//这一行报错
}
}
报错原因:
Collections.addAll(wordsCharacter, list.get(i).toCharArray());
^
required: java.util.Collection<? super T>,T[]
found: java.util.ArrayList<java.lang.Character>,char[]
reason: inferred type does not conform to upper bound(s)
inferred: char[]
upper bound(s): java.lang.Character,java.lang.Object
我想把string转化成charArray然后添加到wordsCharacter这个ArrayList里,为什么报错?