Java 如何在ArrayList的Arraylist中添加和检索值
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How to add and retrieve the values in Arraylist of ArrayList
提问by manpreetSingh
I know how to createan ArrayListof ArrayList, but how to addnew ArrayListand addvalue to that particular ArrayListand how to retrievethe data from that list.
我知道如何创建一个ArrayList的ArrayList，但如何添加新的ArrayList和增加值，以特定的ArrayList，以及如何检索从列表中的数据。
ArrayList<ArrayList<Integer>> arrayList = new ArrayList<ArrayList<Integer>>();
采纳答案by CoderCroc
how to add new ArrayLists and ADD value to that particular ArrayList and how to RETRIEVE the data form that list.
如何向该特定 ArrayList 添加新的 ArrayLists 和 ADD 值，以及如何从该列表中检索数据。
ArrayList<ArrayList<Integer>> arrayList=new ArrayList<ArrayList<Integer>>();
ArrayList<Integer> newAL= new ArrayList<Integer>();
arrayList.add(newAL);
newAL.add(1);
newAL.add(2);
newAL.clear();
System.out.println(arrayList.get(0));
//Changes persist in your arraylist
So after adding ArrayList you can manipulate newALas ArrayListstores referenceyou don't need to fetch and set element from main arrayList.
因此，在添加 ArrayList 后，您可以将其newAL作为ArrayList存储引用进行操作，而无需从 main 获取和设置元素arrayList。
To retrive data you can Iterate(Use ForEach Loop) over arrayListor you can do following
要检索数据，您可以Iterate（使用ForEach 循环），arrayList或者您可以执行以下操作
Integer List0Item1=arrayList.get(0).get(1);//Get first element of list at 0
arrayList.get(0).set(0, 10);//set 0th element of list at 0 as 10
ArrayList<Integer> list10=arrayList.get(10);//get arraylist at position 10
回答by Ruchira Gayan Ranaweera
You can try this
你可以试试这个
ArrayList<ArrayList<Integer>> arrayList = new ArrayList<>();
ArrayList<Integer> list1=new ArrayList<>();
ArrayList<Integer> list2=new ArrayList<>();
list1.add(1); // add to list
list1.add(2);
list2.add(3);
list2.add(4);
arrayList.add(list1); // add to list of list
arrayList.add(list2);
for(ArrayList<Integer> i:arrayList){ // iterate -list by list
for(Integer integer:i){ //iterate element by element in a list
}
}
You can get element directly
可以直接获取元素
arrayList.get(0).get(0); // 0th list 0th value
adding value to 0th list
将值添加到第 0 个列表
arrayList.get(0).add(1); // 1 will add to 0th index list-list1
回答by Bindumalini KK
It is a list of list where every object of the parent list is in turn a sublist.The code is something like below:
它是一个列表列表，其中父列表的每个对象又是一个子列表。代码如下所示：
List<List<String>> mainList = new ArrayList<List<String>>();
List<String> sublist1 = new ArrayList<String>();
sublist1.add("State");
sublist1.add("Country");
sublist1.add("City");
mainList .add(sublist1);
List<String> sublist2 = new ArrayList<String>();
sublist2.add("Sleep");
sublist2.add("Suspend");
sublist2.add("Wait");
mainList .add(sublist2);
for(List<String> obj:mainList){ // iterate
for(String value:obj){
System.out.println(value);
}
}
}
}
Hope this will help to clear your doubt.
