為了不在資料庫中重複新增資料，新增之前執行去重。使用2個for迴圈，remove執行次數正常，得到的結果卻不正常，返回的list長度為0，沒有執行remove(Index)的時候也被刪除了，在我的for迴圈中我看不出哪裡有問題。使用Iteater執行remove()則正常。誰要是看出for迴圈有問題麻煩指出一下，謝謝！

 public List<File> deleteSameFile(List<File> list1,List<File> list2){
        //兩個集合先自己去重，再兩個集合一起去重
List<File> tmp1 = new 
 
ArrayList<>();
        //需要新增進去，不能只是引用
tmp1.addAll(deleteSameFile(list1));
        List<File> tmp2 = new ArrayList<>();
        tmp2.addAll(deleteSameFile(list2));
        Log.d(TAG, "deleteSameFile: tmpD長度=" + tmp1.size());
        Log.d(TAG, "deleteSameFile: tmpT長度=" + tmp2.size());
        if
 
(tmp1.size()==0){
            return tmp2;
        }

        Iterator<File> iterator = tmp1.iterator();
        Iterator<File> it = tmp2.iterator();
        while (it.hasNext()){
            String name  = it.next().getAbsolutePath();
            Log.d(TAG, "deleteSameFile: name="+name);
            if 
 
(iterator.hasNext()){
                String name2 = iterator.next().getAbsolutePath();
                Log.d(TAG, "deleteSameFile: name2=" + name2);
                if(name.equals(name2)){
                    iterator.remove();
                }
            }
        }
        //用for迴圈執行之後得到的集合長度為0，remove(j)實際只執行了12次
//        for(int i=0; i<tmpT.size(); i++){
//            for(int j=0; j<tmpD.size(); j++){
//                if(tmpT.get(i).getAbsolutePath().equals(tmpD.get(j).getAbsolutePath())){
//                    Log.d(TAG, "兩個引數deleteSameFile: tmpD.get(j)=" +tmpD.get(j));
//                    tmpD.remove(j);
//                   j--;
//                }
//            }
//
//        }
Log.d(TAG, "兩個引數deleteSameFile: tmpD=" + Arrays.toString(tmp1.toArray()));
        Log.d(TAG, "兩個引數deleteSameFile: tmpD的集合長度=" + tmp1.size());
        List<File> resultList = new ArrayList<>();
        if(tmp1.size()>0)
        resultList.addAll(tmp1);
        if(tmp2.size()>0)
        resultList.addAll(tmp2);
        Log.d(TAG, "deleteSameFile: reusltList="+Arrays.toString(resultList.toArray()));
        return resultList;

    }

public List<File> deleteSameFile(List<File> musicList){
    Log.d(TAG, "一個引數deleteSameFile: 集合長度="+musicList.size());
    String name = "用來刪除相同檔案的變數初始化";
    for(int i=0; i<musicList.size(); i++){
        name = musicList.get(i).getAbsolutePath();
        for(int j=i+1; j<musicList.size(); j++){
            if(name.equals(musicList.get(j).getAbsolutePath())){
                musicList.remove(j);
                j--;
                Log.d(TAG, "deleteSameFile: name=" +name);
            }
        }

    }
    Log.d(TAG, "一個引數deleteSameFile: musicList=" + Arrays.deepToString(musicList.toArray()));
    return musicList;
}

用set去重更簡單

/*
方法二：使用set去重 */
public Set<Object> deleteSameFile(Set<Object> set,Set<Object> set2){
    Log.d(TAG, "deleteSameFile: set=" + set.size());
    Log.d(TAG, "deleteSameFile: set2=" + set2.size());
    Set<Object> resutlSet = new LinkedHashSet<>();
    resutlSet.addAll(set);
    resutlSet.addAll(set2);
    Log.d(TAG, "deleteSameFile: resultSet=" + resutlSet.size());
    Iterator<Object> iterator = resutlSet.iterator();
    while(iterator.hasNext()){
        Log.d(TAG, "deleteSameFile: 迭代=" + iterator.next().toString());
    }
    Log.d(TAG, "deleteSameFile: resultSet=" + (Arrays.toString(resutlSet.toArray())));
    return resutlSet;
}