How to concatenate two arraylist<String> and store into third arraylist<String>?

Question

I am having three arraylist,Here I have to concatenate 2 arraylist and display it into third arraylist.My coding is given below,

Coding::

List<String> firstName  = new ArrayList<String>();
List<String> lastName  = new ArrayList<String>();
         /////inserting first name
         String string1 = "aaa";
         firstName.add(string1);
         String string2 = "bbb";
         firstName.add(string2);
         ///////inserting last name
         String string3 = "yyy";
         lastName.add(string3);
         String string4 = "zzz";
         lastName.add(string4);

 /////////first name 
        Iterator<String> iterator = firstName.iterator();
        while(iterator.hasNext()){
         String FirstName = iterator.next();
         System.out.println(" FirstName   "+FirstName);
        }
 //////////////last name
        Iterator<String> iterator1 = lastName.iterator();
        while(iterator1.hasNext()){
         String LastName = iterator1.next();
         System.out.println(" LastName  "+LastName);
        }
List<String> name=new ArrayList<String>();
        ///////////name=firstname+lastname
        Iterator<String> iterator11 = lastName.iterator();
        while(iterator11.hasNext()){
         name=firstName+lastName;///////here getting error
               ////////////what should I do here to add two arraylist<String> value
         System.out.println(" Name = FirstName+LastName  "+name);
        }

Output I want::

FirstName   aaa
FirstName   bbb
LastName  yyy
LastName  zzz
Name = FirstName+LastName aaayyy
Name = FirstName+LastName bbbzzz

But I dont know how to concatenate two arrayList and display it in the third arrayList,Please help me.. thanks in advance ..

opyate · Accepted Answer · 2012-06-18 11:59:14Z

7

If the lists have equal size, you can iterate them together:

Iterator<String> iterator = firstName.iterator();
Iterator<String> iterator1 = lastName.iterator();

while(iterator.hasNext() && iterator1.hasNext()){
    String FirstName = iterator.next();
    String LastName = iterator1.next();
    // add FirstName and LastName to the new list here
}

UPDATE

Iterator<String> iterator = firstName.iterator();
Iterator<String> iterator1 = lastName.iterator();
List<String> newList = new ArrayList<String>();

while(iterator.hasNext() && iterator1.hasNext()){
    String FirstName = iterator.next();
    String LastName = iterator1.next();
    newList.add(FirstName + " " + LastName);
}

edited Jun 18, 2012 at 11:59

answered Jun 18, 2012 at 9:26

opyate

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5 Comments

Vlad Over a year ago

didactic +1 for not including the complete solution

user1443848 Over a year ago

I am getting output like [aaa, bbb, yyy, zzz], but i need output like aaayyy bbbzzz

opyate Over a year ago

newList.add(FirstName + " " + LastName);

user1443848 Over a year ago

I am not getting output like aaayyy bbbzzz,getting error that FirstName FirstName not decleared, whgile i used newList.add(FirstName + " " + LastName); where i have to code.. little confusion over here.. thanks in advance

opyate Over a year ago

OK, I've updated my answer with the bits you're struggling with.

Habib · Accepted Answer · 2012-06-18 10:15:53Z

4

List<String> newList = new ArrayList<String>(firstName);
newList.addAll(lastName);

newList will contain elements from firstName and LastName

EDIT: Above code is concatenating the two list, adding lastname at the end of firstname list. If length of your lists are same then you can try:

List<String> newList = new ArrayList<String>();
for(int i=0;i<fistName.length();i++)
{
    newList.Add(firstName.get(i)+lastName.get(i));
}

Iterator<String> iter = newList.iterator();
while(iter.hasNext()){
    System.out.println(" Name = FirstName+LastName  "+iter.next());
    }

This will give you the list you want.

edited Jun 18, 2012 at 10:15

answered Jun 18, 2012 at 9:23

Habib

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3 Comments

user1443848 Over a year ago

I am getting output like [aaa, bbb, yyy, zzz], but i need output like aaayyy bbbzzz

Habib Over a year ago

@user1443848, opyate, answer is correct, I read your title of the question and replied, Its concatenating the two list, adding lastname at the end of first name, that is why you are getting this error.

user1443848 Over a year ago

I am getting error like first name not declared, even though i declared it as arraylist

plucury · Accepted Answer · 2012-06-18 10:20:48Z

1

You should do it by loop.

List<String> name=new ArrayList<String>();
for(i=0;i<firstname.length()&&i<lastname.length();i++){
    name.add(firstname.get(i) + lastname.get(i));
}

edited Jun 18, 2012 at 10:20

answered Jun 18, 2012 at 9:27

plucury

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Comments

Stephen C · Accepted Answer · 2012-06-18 09:29:26Z

0

So you really want to create a list of strings formed by the pair-wise concatenation of the elements of two other lists.

The simplest way is just to write a loop;

 ArrayList<String> l1 = ...
 ArrayList<String> l2 = ...
 ArrayList<String> l3 = new ArrayList<String>(l1.size());
 for (int i =- 0; i < l3.size(); i++) {
     l3.add(l1.get(i) + l2.get(i));
 }

This assumes that l1 and l2 have the same length. (Note: I'm deliberately using the list implementation class in the declarations here, because this code is only appropriate if you are using an ArrayList. For a LinkedList you need to use the list iterators because get(i) is expensive.)

answered Jun 18, 2012 at 9:29

Stephen C

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1 Comment

Thihara Over a year ago

Dude isn't for loops of that style for iteration gone now? Its for..each era!!

amicngh · Accepted Answer · 2012-06-18 09:39:54Z

public static void main(String[] args) {

    List<String> firstName = new ArrayList<String>();
    List<String> lastName = new ArrayList<String>();
    String string1 = "aaa";
    firstName.add(string1);
    String string2 = "bbb";
    firstName.add(string2);
    // /////inserting last name
    String string3 = "yyy";
    lastName.add(string3);
    String string4 = "zzz";
    lastName.add(string4);

    Iterator<String> iterator = firstName.iterator();
    Iterator<String> iterator1 = lastName.iterator();
    List<String> name = new ArrayList<String>();


    while (iterator.hasNext()&& iterator1.hasNext() ) {

        name.add(iterator.next()+" "+iterator1.next());
    }

    Iterator<String> iterator11 = name.iterator();
    while(iterator11.hasNext())
        System.out.println(iterator11.next());

}

Deepak Goswami · Accepted Answer · 2014-12-19 18:14:21Z

0

ArrayList<String> fname=new ArrayList<String>();
fname.add("deepak");
fname.add("avinash");
fname.add("amit");
ArrayList<String> lname=new ArrayList<String>();
lname.add("goswami");
lname.add("singh");
lname.add("jha");
ArrayList<String> name=new ArrayList<String>();
Iterator<String> it1=fname.iterator();
Iterator<String> it2=lname.iterator();
while(it1.hasNext() && it2.hasNext()){
    String f=it1.next();
    String l=it2.next();
    name.add(f+" "+l);
}
for(String str:name){
    System.out.println(str);
}

} }

output :

deepak goswami avinash singh amit jha

edited Dec 19, 2014 at 18:14

answered Dec 19, 2014 at 18:08

Deepak Goswami

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1 Comment

Sam Hanley Over a year ago

This answer would be more useful if it included some non-code text explaining what you're doing here. A code-only answer is only half complete.

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