c++代码翻译成java......，在位大神帮忙翻译下，搞不懂vector...

#include <bits/stdc++.h>
using namespace std;

vector<int> v[100010];
bool vis[100010];


int dfs(int n)
{
    if ( vis[n] )return 0;
    vis[n] = true;
    int sum = 1;
    int size = v[n].size();

    for(int i = 0; i < size; i++ )
    {
        if ( vis[v[n][i]] )continue;
        sum += dfs(v[n][i]);
    }
    return sum;
}

int main(int argc, char const *argv[])
{
    int n;
    while( cin >> n )
    {
        if ( n == 1 )
        {
            cout << 1 << endl;
            continue;
        }
        for(int i = 0; i < n-1; i++ )
        {
            int a,b;
            cin >> a >> b;
            v[a].push_back(b);
            v[b].push_back(a);
        }
        int size = v[1].size();
        int ans = 0;
        memset(vis, false, sizeof(vis));
        vis[1] = true;
        for(int i = 0; i < size; i++ )
        {
            int t = dfs(v[1][i]);
            ans = max(ans, t);
        }
        cout << ans << endl;
    }
    return 0;
}

vector用ArrayList代替
push_back用add函数代替