我试图从现有的ArrayList创建一个ArrayList数组,该ArrayList包含ArrayList中的所有项目,但是按ArrayList数组中的项目名进行排序。这里是我的问题的可视化:
ArrayList<Data>:
[String name0, ...]
[String name0, ...]
[String name1, ...]
[String name0, ...]
[String name1, ...]
...
->
ArrayList<ArrayList<Data>>:
0. ArrayList: 1. ArrayList: ...
[String name0, ...] [String name1, ...]
[String name0, ...] [String name1, ...]
[String name0, ...]
... ...
这是我已经做过的事情:
private ArrayList<Data> data = new ArrayList<>();
private ArrayList<ArrayList<Data>> separatedData = new ArrayList<>();
private List<String> projectnames = new ArrayList<>();
private DataManager dataManager;
public void GenerateDataArrays() throws IOException {
//adds value to allData
allData = dataManager.ReadData("data.csv");
//get all project names out of the ArrayList and adds it to the
List projectnames
for (Data data : allData) {
if (!projectnames.contains(data.getProject())) {
projectnames.add(data.getProject());
}
}
//init new temporary ArrayList
ArrayList<Data> pList = new ArrayList<>();
//clears seperatedData because the method is called everytime a
//button is pressed to reload all data
separatedData.clear();
//looks for all Arrays in the Arraylist with the same name and
//adds each with an equal name to same list
for (String name : projectnames) {
pList.clear();
for(Data data : allData){
if (data.getProject().equals(name)){
pList.add(data);
}
}
seperatedData.add(pList);
}
}
dataManager只读取如下所示的CSV文件:
"name","boolean1","amount","boolean2","date1","date2","date3","shop","reason","person","boolean3"
"SampleName","false","90.0","true","29.04.2019","29.04.2019","29.04.2019","Sampleshop","SampleReason","SamplePerson","true"
"SampleName","false","10.0","false","29.04.2019","29.04.2019","29.04.2019","Sampleshop","SampleReason","SamplePerson","true"
"SampleName2","false","90.0","false","29.04.2019","29.04.2019","29.04.2019","Sampleshop2","SampleReason2","SamplePerson2","true"
"LastProject","false","90.0","false","29.04.2019","29.04.2019","29.04.2019","Sampleshop","SampleReason","SamplePerson","true"
"LastProject","false","60.0","false","29.04.2019","29.04.2019","29.04.2019","Sampleshop","SampleReason","SamplePerson","true"
并将其添加到由ReadData()返回的ArrayList中。
但是当我通过执行以下操作调用ArrayList Array'分离的数据'来接收每个'数据'的'名称'和'金额'时:
for (ArrayList<Data> dataAll : separatedData){
for(Data data : dataAll){
System.out.println(data.getProject() + ", " + data.getAmount());
}
}
我收到了这个:
LastProject, 90.0
LastProject, 60.0
LastProject, 90.0
LastProject, 60.0
LastProject, 90.0
LastProject, 60.0
这是1.只有最新添加的项目和2.初始数量的三倍(ArrayList allData很好)
问题在于:
ArrayList<Data> pList = new ArrayList<>();
separatedData.clear();
for (String name : projectnames) {
pList.clear();
for(Data data : allData){
if (data.getProject().equals(name)){
pList.add(data);
}
}
seperatedData.add(pList);
}
你只需要创建一个由ArrayList
引用的plist
,并且你在for循环中不断清除相同的ArrayList
。此外,你添加相同的引用ArrayList
到你的separatedData
。最后你有ArrayList
包含对同一ArrayList
的多个引用。正如@BlackPearl所建议的那样,解决方案是每次在for循环中创建一个新列表:
for (String name : projectnames) {
ArrayList<Data> pList = new ArrayList<>();
for(Data data : allData){
if (data.getProject().equals(name)){
pList.add(data);
}
}
seperatedData.add(pList);
}