Develop Reference

How to get first value from list of list in java

How can I get first string value from list of list.(i'm not a java expert)
private List<ListView> listView;
listView= List.of(firstlist(), secondlist(), thirdlist())
private List<ListView> firstlist;
private List<ListView> secondlist;
private List<ListView> thirdlist;
firstlist(){"mango", "Apple", "Ornage"}
secondlist(){"book", "pen", "pencil"}
thirdlist(){"van", "car", "lorry"}
Here listview list contains three more lists[i.e firstlist(), secondlist(), thirdlist()]
I need to get first value of all three lists and store it in a Arraylist. I have tried something like,
List listViewTitle = new ArrayList<>(listView.forEach(sublist -> sublist.getFirstValue()));
But it did not work out. I need to take first string from each iterator in the list of list. I need to take mango, book,van and store to the listViewTitle Arraylist

import java.util.List;
import java.util.stream.Collectors;
public class Application {
public static void main(String[] args) {
List<List<String>> list = List.of(List.of("A1","B1"),List.of("A2","B2"));
List<String> listOnlyFirstOne = list
.stream() // create a stream
.map(subList -> subList.get(0)) // collect only first one of each list
.collect(Collectors.toList()); // collect result from map into new list
listOnlyFirstOne.forEach(System.out::println); // print new list
}
}

List<String> listViewTitle = new ArrayList<>();
listView.forEach(sublist -> listViewTitle.add(sublist.get(0)));

How do I convert an array of strings into append-able list?

I have parsed through a CSV file and stored it as an array of strings. I'd like to add an item to each sub-array if certain conditions have been met, as shown below. However, I am not able to use the .add() method and get a "Cannot resolve method" message in my IDE. To try to get around this, I attempted to create a new arraylist in which I placed the contents of the string array, but the problem persisted. How do I make it so that I can add an item to each sublist?
import java.util.List;
import java.util.ArrayList;
public class Application {
/**
* Main entry of the application.
*
* #param args This should be empty
*/
public static void main(final String[] args) {
String csvFile = "/IUCNListV2.csv";
List<String[]> listAnimal =
ReadCSV.readFileAndParseSkipFirstline(Application.class.getResourceAsStream(csvFile));
List<String[]> list2 = new ArrayList<>();
for (String [] text : listAnimal) {
list2.add(text);
}
for(String[] subList: list2)
if (null != subList && subList[4].equals("x") &&
subList[5].equals("y")) {
subList.add("z");
}
}
}

You can't add element in string array directly. You can follow those steps
You can create list from string array
Add the element in list
Again convert list to array
Update the outer list
for (int i = 0; i < list2.size(); i++) {
String[] subList = list2.get(i);
if (null != subList && subList[4].equals("x") &&
subList[5].equals("y")) {
ArrayList<String> list = new ArrayList<>(Arrays.asList(subList)); // create a list
list.add("z"); // add in list
list2.set(i, list.toArray(new String[0])) // create array from list and update parent list
}
}
Or create a List<List<String>> from List<String[]> first then add in inner list

To convert an array of String to ArrayList simply use this
String[] x = {"example1","example2"};
ArrayList<String> list = new ArrayList<>(Arrays.asList(x));

You can't use the add method on arrays, because the add method is in the List interface, but you can use List objects in your other list like this, for this solution:
public class Application {
/**
* Main entry of the application.
*
* #param args This should be empty
*/
public static void main(final String[] args) {
String csvFile = "/IUCNListV2.csv";
List<List<String>> listAnimal =
ReadCSV.readFileAndParseSkipFirstline(Application.class.getResourceAsStream(csvFile));
List<List<String>> list2 = new ArrayList<>();
list2.addAll(listAnimal);
for(List<String> subList: list2)
if (null != subList && subList.get(4).equals("x") &&
subList.get(5).equals("y")) {
subList.add("z");
}
}
}

Display ArrayList of char in Java

I am working on the first part of a String permutation problem and I am just looping over the first char of a string and swap it with every following char of that same String. I initialized an empty ArrayList to store all of those permutations called listeFinale. When I am printing that ArrayList, I am getting a collection of object and not values ([[C#61bbe9ba, [C#61bbe9ba, [C#61bbe9ba, [C#61bbe9ba]), how can I print each char stored in the ArrayList?
import java.util.ArrayList;
import java.util.List;
public class checkPermu {
public static void main(String[] args) {
String myString = "aabc";
applyPermu(myString);
}
public static void applyPermu(String toCheck){
char[] newString = toCheck.toCharArray();
List listeFinale = new ArrayList();
for(int i = 0 ; i < newString.length ; i ++){
char temp = newString[0];
newString[0] = newString[i];
newString[i] = temp;
listeFinale.add(newString);
System.out.println(listeFinale);
}
}
}

First of all, don't use raw types for your List please.. Change:
List listeFinale = new ArrayList();
to:
List<char[]> listeFinale = new ArrayList<>();
As for your actual problem. Those values you see are the default toString() outputs of your inner character-arrays. You could iterate over your list, and call the java.util.Arrays.toString(char[]) method for them like this:
listeFinale.forEach(arr -> System.out.println(Arrays.toString(arr)));
Or, if you want to print them back as String again, use new String(char[]):
listeFinale.forEach(arr -> System.out.println(new String(arr)));
Try it online.

How to get an String and the ArrayList stored in a Arraylist of objects of a class using Java stream

I have modified the code and trying to get an ArrayList and the String stored in an Arraylist of Objects on a specific condition(say 'str' string equal to 2). I'm not able to convert the Stream to ArrayList. Please help me understand what needs to be done to get the ArrayList from this stream.
I have a class 'SampleClass' like below:
import java.util.ArrayList;
public class SampleClass {
String str;
ArrayList<String> al;
String check;
public SampleClass(String str, ArrayList<String> al, String check) {
super();
this.str = str;
this.al = al;
this.check = check;
}
public String getStr() {
return str;
}
public void setStr(String str) {
this.str = str;
}
public ArrayList<String> getAl() {
return al;
}
public void setAl(ArrayList<String> al) {
this.al = al;
}
public String getCheck() {
return check;
}
public void setCheck(String check) {
this.check = check;
}
}
I have another class 'GetTheArrayListStoredInAnotherArrayList' like below where I'm trying to get the ArrayList stored inside the ArrayList of objects. Please correct me where I'm wrong.
import java.util.ArrayList;
import java.util.Arrays;
import java.util.stream.Collectors;
public class GetTheArrayListStoredInAnotherArrayList{
public static void main(String[] args) {
String test = "qw,rer,try,try,erh5,wertgw45t,45";
ArrayList<String> al = new ArrayList<String>();
al.addAll(new ArrayList<String>(Arrays.asList(test.split(","))));
System.out.println(al);
ArrayList<SampleClass> sca = new ArrayList<SampleClass>();
SampleClass sc1 = new SampleClass("1", al,"ch1");
SampleClass sc2 = new SampleClass("2", al,"cc2");
SampleClass sc3 = new SampleClass("3", al,"fr3");
SampleClass sc4 = new SampleClass("4", al,"fg4");
sca.add(sc1);
sca.add(sc2);
sca.add(sc3);
sca.add(sc4);
ArrayList<String> als1 = null;
ArrayList<String> als = sca.stream().filter( s -> s.getStr().equals("2")).flatMap(sc -> sc.getAl().stream()).collect(Collectors.toCollection(ArrayList::new));
System.out.println(als);
String ch = (String) sca.stream().filter(s -> s.getStr().equals("1")).map(ac -> ac.getCheck());
System.out.println(ch);
}
}
I got the below error when I executed the code :
Exception in thread "main" java.lang.Error: Unresolved compilation problem:
Cannot cast from Stream<String> to String
at GetTheArrayListStoredInAnotherArrayList.main(GetTheArrayListStoredInAnotherArrayList.java:24)

Not entirely sure what you are trying to do, but you need to change your code a bit:
List<String> als = sca.stream()
.filter(s -> s.getStr().equals("2"))
.flatMap(sc -> sc.getAl().stream())
.collect(Collectors.toList());
A few things :
flatMap must return a Stream (in your case you are returning a List)
Collectors.toList makes no guarantee of the List in returns, so the assignment is to a List, not an ArrayList.
EDIT
This:
Stream<String> stream = sca.stream().filter(s -> s.getStr().equals("1"))
.map(ac -> ac.getCheck());
Will produce a Stream<String>. You can't simply cast that to a String, you have to collect/reduce that to whatever you want. Like let's say a List:
List<String> list = sca.stream()
.filter(s -> s.getStr().equals("1"))
.map(ac -> ac.getCheck())
.collect(Collectors.toList());
Or a single String for example:
String r = sca.stream()
.filter(s -> s.getStr().equals("1"))
.map(ac -> ac.getCheck())
.collect(Collectors.joining(","));
This is actually basic stuff... you should really study some samples and the documentation.

Change
ArrayList<String> als = sca.stream().filter( s -> s.getStr().equals("2")).flatMap( sc -> sc.getAl());
To
ArrayList<String> als = sca.get(0).getAl();

First you have to use List instead of ArrayList. So with List you code will looks like
List<String> als1 = null;
List<String> als = sca.stream().
filter(s -> s.getStr().equals("2")). //Comparing
map(s -> s.getAl()) // Converting List<SampleClass> to list of all al list inside all SampleClass in format List<List<Straing>>
.flatMap(ArrayList::stream) //Creating a flat list from list of list of List :: List<List<Straing>> --To--> List<String>
.collect(Collectors.toList()); // Collecting as list
I have commented this code with details. But here if there are two SampleCalss objects in the list with str=2 then it will merge the al list of both objects. hope it will help you .

I'm trying to get the ArrayList stored inside the ArrayList of objects.
Well, the basic algorithm is as follows: Filter sca so it only leaves elements where str is "2" -> Get a single element from all the left over elements -> Get the al stored inside of that element.
You have done the first part correctly:
sca.stream().filter( s -> s.getStr().equals("2"))
But now you need to get a single element from the filtered result (filter can result in multiple elements being left over), so you call findFirst:
.findFirst().get()
This get call will throw an exception if there is no element left after the filter. If you don't want it to throw an exception, you can replace it with an orElse call:
.findFirst.orElse(new SampleClass("", null))
If you use orElse, the method chain will evaluate to null if no element with str being "2".
Now you just need to get the array list by calling getAl():
.getAl();
Now we combine all this together:
ArrayList<String> als = sca.stream()
.filter( s -> s.getStr().equals("2"))
.findFirst().orElse(new SampleClass("", null)).getAl();

Java:HashMap<String,String> storing same value as key and value.?

I am getting this strange output in HashMap.
I have two ArrayList<String> one containing the key and another containing value.
My HashMap<String,String> will store only string as key and value pair. But key itself is getting stored in value. I have checked my value arraylist, it's printing the value. But during putting it's setting it as key itself.
Code snippet is:
public HashMap<String,String> getLstBarring()
{
ArrayList<String> temparrLst=setPreParameters(fetchPreDetails, 1);
System.out.println("KEY" + temparrLst);
ArrayList<String> tempArrLstId=setPreParameters(fetchPreDetails, 14);
System.out.println("VALUE" +tempArrLstId);
int length=tempArrLstId.size();
for(int index=0;index<length;index++)
{
System.out.println("VALUE IN KEY" + temparrLst.get(index));
System.out.println("VALUE IN VALUE" + tempArrLstId.get(index));
this.lstBarring.put(temparrLst.get(index), tempArrLstId.get(index));
}
System.out.println("INSIDE ODB....>>>>>>>>>>>>>>" + lstBarring);
return this.lstBarring;
}
Problem is:
1st SOP is KEY-printing all the key correctly.
2nd SOP is VALUE-printing all the value correctly.
3rd SOP is VALUE IN KEY----printing all the values.
4th SOP is VALUE IN VALUE--printing all the values.
Hence after ever iteration I am getting value,value in HashMap whereas it should be key,value.
Here's look at my Method:-
public ArrayList<String> setPreParameters(HashMap<Integer,String> fetchPreDetails,int index)
{
switch(index)
{
case 1:
{
arrLstData.clear();
splittedString=fetchPreDetails.get(1).split(",");
Collections.addAll(arrLstData, splittedString);
break;
}
return arrLstData;
Please guide me as to where am I going wrong.

My guess is that either fetchPreDetails is a collection being mutated by setPreParameters() or else setPreParameters() is mutating some other shared state so that the collection referenced by your temparrLst is being changed on the second call to setPreParameters(). I.e.
List<String> strings = new ArrayList();
strings.add("a");
strings.add("b");
List<String> otherStrings = strings;
otherStrings.add("c");
I expect your code assumes that strings would contain "a" and "b" and that otherStrings would contain "a", "b", and "c". This isn't how object references work in Java. The line List<String> otherStrings = strings; makes both strings and otherStrings point to the same collection, and thus changes made using either name affect the same thing.
Edit: Your newly-posted code seems to prove my hypothesis. You have a variable called arrLstData that you clear, populate, and return on each call to setPreParameters(). You're returning the same collection every time you call this method. Therefore you just have multiple handles to the same collection instead of multiple collections. You need to create a new collection and return it each time you call setPreParameters().
Edit again: Maybe this will make it clearer. Here's what you're doing:
public static void main(String[] args) {
Foo f = new Foo();
List<String> list1 = f.getList("a", "b");
System.out.println(list1);
List<String> list2 = f.getList("c", "d");
System.out.println(list2);
System.out.println(list1);
}
static class Foo {
private List<String> myList = new ArrayList<String>();
public List<String> getList(String... strings) {
myList.clear();
myList.addAll(Arrays.asList(strings));
return myList;
}
}
Note that this exhibits exactly the behavior that you're describing, and the correct way to solve it is something like this:
public static void main(String[] args) {
Foo f = new Foo();
List<String> list1 = f.getList("a", "b");
System.out.println(list1);
List<String> list2 = f.getList("c", "d");
System.out.println(list2);
System.out.println(list1);
}
static class Foo {
public List<String> getList(String... strings) {
List<String> result = new ArrayList<String>();
result.addAll(Arrays.asList(strings));
return result;
}
}

You are reusing the same List over and over at your setPreParameters Method.
The List in arrLstData is returned and stored in temparrLst, now you are clearing the the Lists content, putting new stuff in it and storing it to tempArrLstId.
Now the three variables all contain the very same list (they are not equals, its the same!).
There is only one List object at the whole example!
Its like you got a box and label it "A" on one side put stuff in it, label it "B" on another side and wondering why the box "B" is empty when you turn box "A" upside-down.

Did you maybe mean something like this?
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class GlobalsMess {
private Map<String, String> lstBarring = new HashMap<String, String>();
private Map<Integer, String> fetchPreDetails = new HashMap<Integer, String>();
public GlobalsMess() {
fetchPreDetails.put(1, "john,vikam,david");
fetchPreDetails.put(14, "1,2,3");
}
public Map<String, String> getLstBarring() {
List<String> tempKeys = setPreParameters(fetchPreDetails.get(1));
System.out.println("KEY" + tempKeys);
List<String> tempIds = setPreParameters(fetchPreDetails.get(14));
System.out.println("VALUE" + tempIds);
for (int index = 0; index < tempIds.size(); index++) {
System.out.println("VALUE IN KEY" + tempKeys.get(index));
System.out.println("VALUE IN VALUE" + tempIds.get(index));
this.lstBarring.put(tempKeys.get(index), tempIds.get(index));
}
System.out.println("INSIDE ODB....>>>>>>>>>>>>>>" + lstBarring);
return this.lstBarring;
}
public List<String> setPreParameters(String fetchPreDetailsValue) {
List<String> arrLstData = new ArrayList<String>();
Collections.addAll(arrLstData, fetchPreDetailsValue.split(","));
return arrLstData;
}
public static void main(String[] args) {
new GlobalsMess().getLstBarring();
}
}
Output:
KEY[john, vikam, david]
VALUE[1, 2, 3]
VALUE IN KEYjohn
VALUE IN VALUE1
VALUE IN KEYvikam
VALUE IN VALUE2
VALUE IN KEYdavid
VALUE IN VALUE3
INSIDE ODB....>>>>>>>>>>>>>>{david=3, vikam=2, john=1}