This is the initalization.
ArrayList<ArrayList<String>> names = new ArrayList<ArrayList<String>>();
The functions are as follow.
names.add("Amey");
and
names.set(a, "Jane");
Here is the full program that needs to be turned into a 2D ArrayList. The purpose of the program is to replace John with Jane, wherever John is.
import java.util.*;
public class Prac5twodArraylistString {
public static void main(String[] args) {
ArrayList<ArrayList<String>> names = new ArrayList<ArrayList<String>>();
names.add("Amey");
names.add("Aditya");
names.add("John");
names.add("Saideep");
names.add("Shrikar");
names.add("Sujay");
for (int a = 0; a <= (names.size()) - 1; a++) {
System.out.println(names.get(a));
}
for (int a = 0; a <= (names.size()) - 1; a++) {
if (names.get(a).equals("John")) {
names.set(a, "Jane");
}
}
for (int a = 0; a <= (names.size()) - 1; a++) {
System.out.println(names.get(a));
}
}
}
.Will you please help me with this code?
Your code won't compile. You are creating a List of a List of String and you are trying to add just a String to it instead of a List of String.
When you do names.add("anyName"); you would need to do names.add(new ArrayList<String>() {{add("name")};. But then the rest of your code won't work.
If you change
ArrayList<ArrayList<String>> names = new ArrayList<ArrayList<String>>();
for
ArrayList<String> names = new ArrayList<>();
your code will compile and work.
By my understanding I feel that your problem lies with your 2D ArrayList. The line ArrayList<ArrayList<String>> names = new ArrayList<ArrayList<String>>(); means that you variable names is actually an ArrayList of other ArrayList<String>. So your code name.add("SomeString") will show an error as the parameter expected in this method is ArrayList<String> but you are supplying it with String.
Now If you require to have an ArrayList of ArrayList Then you have to declare an new variable of ArrayList<String> Like this:
ArrayList<String> temp = new ArrayList<>();
The add the names to this temp object like this instead of the name object:
temp.add("Amey");
temp.add("Aditya");
temp.add("John");
temp.add("Saideep");
temp.add("Shrikar");
temp.add("Sujay");
Now add this temp object to the names object like this:
names.add(temp);
For printing out your contents you have to use this loop:
for(ArrayList<String> a : names){
for(String name: a){
System.out.println(name);
}
}
For replacing "John" with "Jane" you could use the following:
for(ArrayList<String> a : names){
if(a.contains("John")){
a.set(a.indexOf("John"), "Jane");
}
}
Related
I need to check if all Strings from ArrayList are present in another ArrayList. I can use containsAll but this is not what I want to achieve. Let's me show you this on example:
assertThat(firstArray).containsAll(secondArray);
This code will check if all items from one array is in another one. But I need to check that every single item from one array is contained in any place in the second array.
List<String> firstArray = new ArrayList<>;
List<String> secondArray = new ArrayList<>;
firstArray.add("Bari 1908")
firstArray.add("Sheffield United")
firstArray.add("Crystal Palace")
secondArray.add("Bari")
secondArray.add("Sheffield U")
secondArray.add("C Palace")
So I want to check if first item from secondArray is in firstArray(true) than that second(true) and third(false). I wrote the code which is doing this job but it's quite complicated and I would like to know if there is any simpler way to achieve this goal (maybe with using hamcrest matchers or something like that)
ArrayList<String> notMatchedTeam = new ArrayList<>();
for (int i = 0; i < secondArray.size(); i++) {
String team = secondArray.get(i);
boolean teamMatched = false;
for (int j = 0; j < firstArray.size(); j++) {
teamMatched = firstArray.get(j).contains(team);
if (teamMatched) {
break;
}
}
if (!teamMatched) {
notMatchedTeam.add(team);
}
}
You can do something like this
List<String> firstArray = new ArrayList<>();
List<String> secondArray = new ArrayList<>();
firstArray.add("Bari 1908");
firstArray.add("Sheffield United");
firstArray.add("Crystal Palace");
secondArray.add("Bari");
secondArray.add("Sheffield U");
secondArray.add("C Palace");
Set<String> firstSet= firstArray
.stream()
.collect(Collectors.toSet());
long count= secondArray.stream().filter(x->firstSet.contains(x)).count();
///
Map<String, Boolean> result =
secondArray.stream().collect(Collectors.toMap(s->s, firstSet::contains));
If count >0, then there are some items in second array which are not there in first.
result contains the string with its status.
Thanks
If you have space concerns like you have millions of words in one file and need to check entry of second file in first then use trie. From first make trie and check every entry of second in first.
Situation:
In your question you said that you wanted to return for each element if it exists or not, and in your actual code you are only returning a list of matching elements.
Solution:
You need to return a list of Boolean results instead, this is the code you need:
public static List<Boolean> whichElementsFound(List<String> firstList, List<String> secondList){
ArrayList<Boolean> resultList = new ArrayList<>();
for (int i = 0; i < secondList.size(); i++) {
String team = secondList.get(i);
resultList.add(firstList.contains(team));
}
return resultList;
}
Demo:
This is a working Demo using this method, returning respectively a List<Boolean> to reflects which element from the first list are found in the second.
Edit:
If you want to return the list of elements that were not found, use the following code:
public static List<String> whichElementsAreNotFound(List<String> firstList, List<String> secondList){
ArrayList<String> resultList = new ArrayList<>();
for (int i = 0; i < secondList.size(); i++) {
String team = secondList.get(i);
if(!firstList.contains(team)){
resultList.add(team);
}
}
return resultList;
}
This is the Demo updated.
Lets say you have an array like this: String[] theWords = {"hello", "good bye", "tomorrow"}. I want to remove/ignore all the strings in the array that have the letter 'e'. How would I go about doing that? My thinking is to go:
for (int arrPos = 0; arrPos < theWords.length; arrPos++) { //Go through the array
for (int charPos = 0; charPos < theWords[arrPos].length(); charPos++) { //Go through the strings in the array
if (!((theWords[arrPos].charAt(charPos) == 'e')) { //Finds 'e' in the strings
//Put the words that don't have any 'e' into a new array;
//This is where I'm stuck
}
}
}
I'm not sure if my logic works and if I'm even on the right track. Any responses would be helpful. Many thanks.
One easy way to filter an array is to populate an ArrayList with if in a for-each loop:
List<String> noEs = new ArrayList<>();
for (String word : theWords) {
if (!word.contains("e")) {
noEs.add(word);
}
}
Another way in Java 8 is to use Collection#removeIf:
List<String> noEs = new ArrayList<>(Arrays.asList(theWords));
noEs.removeIf(word -> word.contains("e"));
Or use Stream#filter:
String[] noEs = Arrays.stream(theWords)
.filter(word -> !word.contains("e"))
.toArray(String[]::new);
You can directly use contains() method of String class to check if "e" is present in your string. That will save your extra for loop.
It would be simple if you use ArrayList.
importing import java.util.ArrayList;
ArrayList<String> theWords = new ArrayList<String>();
ArrayList<String> yourNewArray = new ArrayList<String>;//Initializing you new array
theWords.add("hello");
theWords.add("good bye");
theWords.add("tommorow");
for (int arrPos = 0; arrPos < theWords.size(); arrPos++) { //Go through the array
if(!theWords.get(arrPos).contains("e")){
yourNewArray.add(theWords.get(arrPos));// Adding non-e containing string into your new array
}
}
The problem you have is that you need to declare and instantiate the String array before you even know how many elements are going to be in it (since you wouldn't know how many strings would not contain 'e' before going through the loop).
Instead, if you use an ArrayList you do not need to know the required size beforehand. Here is my code from start to end.
String[] theWords = { "hello", "good bye", "tomorrow" };
//creating a new ArrayList object
ArrayList<String> myList = new ArrayList<String>();
//adding the corresponding array contents to the list.
//myList and theWords point to different locations in the memory.
for(String str : theWords) {
myList.add(str);
}
//create a new list containing the items you want to remove
ArrayList<String> removeFromList = new ArrayList<>();
for(String str : myList) {
if(str.contains("e")) {
removeFromList.add(str);
}
}
//now remove those items from the list
myList.removeAll(removeFromList);
//create a new Array based on the size of the list when the strings containing e is removed
//theWords now refers to this new Array.
theWords = new String[myList.size()];
//convert the list to the array
myList.toArray(theWords);
//now theWords array contains only the string(s) not containing 'e'
System.out.println(Arrays.toString(theWords));
I have one arraylist that contain two list
like this
[[asd, asswwde, efef rgg], [asd2223, asswwd2323e, efef343 rgg]]
My Code is
ArrayList<String> create = new ArrayList<String>();
ArrayList<String> inner = new ArrayList<String>();
ArrayList<String> inner1 = new ArrayList<String>();
inner.add("asd");
inner.add("asswwde");
inner.add("efef rgg");
inner1.add("asd2223");
inner1.add("asswwd2323e");
inner1.add("efef343 rgg");
create.add(inner.toString());
create.add(inner1.toString());
i have to get all value one by one of every index of that arraylist
So what is the best way to get these all value one by one.
I am using JAVA with Eclipse Mars.
Just use two nested loops:
List<List<Object>> list = ...;
for (List<Object> subList : list) {
for (Object o : subList) {
//work with o here
}
}
You may also want to consider replacing the inner lists by proper objects.
You want to loop through the outside ArrayList and then loop through each ArrayList within this ArrayList, you can do this by using the following:
for (int i = 0; i < outerArrayList.size(); i++)
{
for (int j = 0; j < outerArrayList.get(i).size(); j++)
{
String element = outerArrayList.get(i).get(j);
}
}
Here is another verison you may find easier to understand, but is essentially the same:
for (int i = 0; i < outerArrayList.size(); i++)
{
ArrayList<String>() innerArrayList = outerArrayList.get(i)
for (int j = 0; j < innerArrayList.size(); j++)
{
String element = innerArrayList.get(j);
}
}
or alternatively again using a foreach loop:
for (ArrayList<String> innerArrayList : outerArrayList)
{
for (String element : innerArrayList)
{
String theElement = element;
}
}
It might be worth noting that your ArrayList appears to contain different types of elements - is this definitely what you wanted to do? Also, make sure you surround your strings with "" unless they are variable names - which it doesn't appear so.
EDIT: Updated elements to type String as per your update.
I would also recommend you change the type of your create ArrayList, like below, as you know it will be storing multiple elements of type ArrayList:
ArrayList<ArrayList> create = new ArrayList<ArrayList>();
Try to use for loop nested in foreach loop like this:
for(List list : arrayListOfList)
{
for(int i= 0; i < list.size();i++){
System.out.println(list.get(i));
}
}
I'm not sure if the data structures are part of the requirements, but it would be better constructed if your outer ArrayList used ArrayList as the generic type.
ArrayList<ArrayList<String>> create = new ArrayList<ArrayList<String>>();
ArrayList<String> inner = new ArrayList<String>();
ArrayList<String> inner1 = new ArrayList<String>();
...
create.add(inner);
create.add(inner1);
Then you could print them out like this:
for(List list : create) {
for (String val : list) {
System.out.println(val);
}
}
Othewise, if you stick with your original code, when you add to the outer list you are using the toString() method on an ArrayList. This will produce a comma delimited string of values surrounded by brackets (ex. [val1, val2]). If you want to actually print out the individual values without the brackets, etc, you will have to convert the string back to an array (or list) doing something like this:
for (String valList : create) {
String[] vals = valList.substring(1, val.length() - 1).split(",");
for (String val : vals) {
System.out.println(val.trim());
}
}
This is my assignment, and I am not sure how to proceed. The output only prints my first four teachers, and I don't know why it isn't printing my last three teachers as well. Thanks!
Create an ArrayList called teachers. Fill the ArrayList with your teacher’s LAST NAMES ONLY in the order that you see them during the day (Period 1: Jensen, Period 2: Houge, Period 3: …, etc.) You only need to put the teacher’s last name in the ArrayList, so it would print [Jensen, Houge, etc…].) Print the ArrayList using a print method.
Write a method that takes your teachers ArrayList, and from it makes a new ArrayList called ordered, whererin your teacher’s names are now in lexicographic order. Print the resulting ArrayList. (DO NOT CHANGE YOUR ORIGINAL ARRAYLIST, MAKE A NEW ONE!)
import java.util.ArrayList;
public class LexicographicOrdering
{
public static void main (String [] args){
ArrayList<String> teachers = new ArrayList<String>();
teachers.add("Turnbow");
teachers.add("Dyvig");
teachers.add("Williams");
teachers.add("Houge");
teachers.add("Allaire");
teachers.add("Violette");
teachers.add("Dorgan");
System.out.println(teachers);
order(teachers);
}
public static void order(ArrayList<String> teachers ){
ArrayList<String> ordered = new ArrayList<String>();
for(int i = 0; i < teachers.size(); i++){
String str = teachers.get(i);
for(int j = 1; j < teachers.size(); j++){
if(str.compareTo(teachers.get(j)) > 0){
str = teachers.get(j);
}
}
ordered.add(str);
teachers.remove(str);
}
System.out.print(ordered);
}
}
So the issue here is with your static order method. As Karl suggests above, you want to break the method into two separate parts. The first will create an ArrayList named 'ordered' and then fill it with the data contained in the 'teachers' array.
ArrayList<String> ordered = new ArrayList(); //the second <String> is not required
for(int i = 0; i < teachers.size(); i++){
String str = teachers.get(i);
ordered.add(str);
}
The next objective is to sort the array in alphabetical order, which can be achieved using the Collections.sort(ArrayList) method which is contained in the java.util package.
Collections.sort(ordered);
And now you need to print the ArrayList.
System.out.println(ordered);
As this is a homework assignment, I would recommend reading up on the Collections.sort() method, along with an example of it. A quick google search pulled up the following website: http://beginnersbook.com/2013/12/how-to-sort-arraylist-in-java/
Also, I would recommend reading the API for the Collection class. https://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#sort-java.util.List-
Edit:
At a quick glance, I would assume the reason that your string is cutting out the last 3 names is due to the fact that you are removing items from the list as you are looking at each position in the list. Essentially, you are looking at every other item in the list because of this.
So I figured it out! I only needed to set the first for loop back to zero. Here is the new code:
import java.util.ArrayList;
public class LexicographicOrdering
{
public static void main (String [] args){
ArrayList<String> teachers = new ArrayList<String>();
teachers.add("Turnbow");
teachers.add("Dyvig");
teachers.add("Williams");
teachers.add("Houge");
teachers.add("Allaire");
teachers.add("Violette");
teachers.add("Dorgan");
System.out.println(teachers);
order(teachers);
}
public static void order(ArrayList<String> teachers ){
ArrayList<String> ordered = new ArrayList<String>();
for(int i = 0; i < teachers.size(); i++){
String str = teachers.get(i);
for(int j = 1; j < teachers.size(); j++){
if(str.compareTo(teachers.get(j)) > 0){
str = teachers.get(j);
}
}
i =- 1;
ordered.add(str);
teachers.remove(str);
}
System.out.print(ordered);
}
}
i have arraylists named sub and main,
ArrayList main = new ArrayList();
ArrayList sub=new ArrayList();
i add value to sub and then add sub to main.
example;
sub.add(1);
sub.add(2);
main.add(sub);
now i want to get all values inside sub
so i used following one but .get(j) gives me the error get >> canot find symbol
for (int i=0;i<main.size();i++) {
System.out.println();
for (int j=0;j<sub().size();j++) {
System.out.print(main.get(i).get(j));//error line
}
}
how can i get all values inside subarray of main arraylist
When you declare a variable as
ArrayList main;
This list holds Objects. This means that main.get(i) will only return an Object, even if you add ArrayLists. That's why you get a compiler error: Object doesn't have a method named get().
To fix the problem, you need to use generics:
ArrayList<List<Integer>> main = new ArrayList<>();
ArrayList<Integer> sub=new ArrayList<>();
Now get() will return a List<Integer> which has a get() method, so the compiler error will disappear.
Generics could be your friend here:
ArrayList<ArrayList<Object>> main = new ArrayList<ArrayList<Object>>(); // or new ArrayList<>(); in Java 7+
ArrayList<Object> sub = new ArrayList<Object>(); // or new ArrayList<>();
If you can't or don't want to use generics, the solution is to cast the expression main.get(i) to an ArrayList first:
System.out.println(((ArrayList) main.get(i)).get(j));
Go through the following code
public class ArrayListDemo {
public static void main(String[] args) {
List<List<Integer>> main = new ArrayList<>();
List<Integer> sub = new ArrayList<>();
sub.add(1);
sub.add(2);
main.add(sub);
//If you want to get values in sub array list
for(int i = 0; i < 1; i++){
List<Integer> arr = main.get(i);
for(Integer val : arr) System.out.println(val + "");
}
//If you want to print all values
for(List<Integer> list : main){
for(Integer val : list) System.out.println(val + "");
}
}
}
In the above code, I had declared an ArrayList (main) to keep all Array which are having Integer values. Also i had declared an another ArrayList (sub) to keep all Integer values.
I had used ArrayList data structure because of length of the List will be changing the
run time.
Good Luck !!!