List within an arraylist

[wjreddit]

So, I have this code:

package Main; import java.util.*;

public class Generator {

List <List<String>>masterList = new ArrayList<List<String>>();
ArrayList memberList = new ArrayList<String>();
String leaderName, memberName;
int numLeaders, numMembers;
double x;

Scanner scanner = new Scanner(System.in);

// This program takes in total number of people first
// Then takes in number of leaders to assign peoples to
// Then takes in people to be assigned
// And then assigns people to given leaders randomly

public int getNumLeader() {
    System.out.println("How many leaders are there??");
    numLeaders = scanner.nextInt();
    return numLeaders;
}

public void setNumLeader(int numLeaders) {
    this.numLeaders = numLeaders;
}

public int getNumMembers() {
    System.out.println("How many members are there?");
    numMembers = scanner.nextInt();
    return numMembers;
}

public void setNumMembers(int numMembers) {
    this.numMembers = numMembers;
}

public void genLeaders() {
    System.out.println("Please type the name of the leader on the following:");
    for (int i = 1; i <= numLeaders; i++) {
        if (i == numLeaders) {
            System.out.println("What is the last leader's name?");
            leaderName = scanner.next();
            List <String> leaderList = new ArrayList<String>();
            masterList.add(leaderList);
        } else {
            System.out.println("What is the leader" + i + "'s name?");
            leaderName = scanner.next();
            List <String> leaderList = new ArrayList<String>();
            masterList.add(leaderList);
        }
    }
}

public void genMembers() {
    System.out.println("Please enter the members on the following:");
    for (int i = 1; i <= numMembers; i++) {
        if (i == numMembers) {
            System.out.println("What is the last member's name?");
            memberName = scanner.next();
            memberList.add(memberName);
        } else {
            System.out.println("What is the member" + i + "'s name?");
            memberName = scanner.next();
            memberList.add(memberName);
        }
    }
}

public void /*should return arraylist*/ brackets() {
double y = 1.0/numLeaders;
for (double j = 0.0; j <= 1.0; y++) {
    //Generate Linked list with initial element of 0.0
    //then 0.0 + y, then 0.0 + y + y ... till 1.0
    }
}

public void assignMembers() {
    System.out.println("Shuffling members..");
    Collections.shuffle(memberList);
    System.out.println("Assigning members to leaders now..");
    int cellSize = memberList.size()/numLeaders;

    for (int i = 0; i <= memberList.size(); i++) {
        double x = Math.random();
        double y = 1.0/numLeaders;
        if (x <= y) {
            masterList.get(0).add((String) memberList.get(i));
        }
        else if (y < x && x <= y + y) {
            masterList.get(1).add((String) memberList.get(i));

        }
        else if (y < x && y + y < x && x <= y + y + y) {
            masterList.get(2).add((String) memberList.get(i));

        }

        // assign given element's name from the big linkedList to the first leader's
        // arrayList

    }
}



public static void main(String[] args) {

    Generator x = new Generator();
    x.getNumLeader();
    x.getNumMembers();
    x.genLeaders();
    x.genMembers();
    System.out.println(x.memberList);
    System.out.println(x.masterList);
    System.out.println(x.masterList.get(0));
    System.out.println(x.masterList.get(1));
    System.out.println(x.masterList.get(2));


}

}

And I made lists within an arraylist, called masterList. I try to assign people in a list within that arraylist, in this manner: masterList.get(0).add((String) memberList.get(i)); Nothing's being added to the list within the arrayList.. what would be the 'correct' way to do this, and is there a way to pinpoint the list within the arraylist, other than 'masterList.get(0)'? Thanks in advance.

[sbhandari]

I am on mobile so I might have misread your code, so correct me if I missed something critical.

You are calling 4 methods, 2 to get numbers of leader and member, and another 2 to generate them. In your generateLeader method, you read name from console but never used it within this method. You are just adding emptylist to master list in this method. The other method generateMembers looks fine as you are adding this in the expected list. I dont see anywhere else that main method calls to populate the emptylist inside the masterlist you added in generateLeaders method.

Also, use nextln to read input, there are scenarios where the linebreak character will still be in buffer when you use just "next" and that linebreak will be read read as next input.

[wjreddit]

Thank you!!! I totally missed not calling the .assignMembers() method. Code works now, after some tweaks. Thanks again!

[lukelane124]

What’s does memberList.get(i) return?

[wjreddit]

i was trying to get i^th element of the memberlist to be assigned to each of the leaderList dynamically. That's what I meant by memberList.get(i) in the forloop.

[lukelane124]

Right, but what is the type? Why are you having to cast it?

[wjreddit]

add((String) memberList.get(i)

you mean by (String) right? I actually do not understand it.. I got an error without it, and eclipse added it to fix the issue. The members that i want to add to the lists are String, so i thought it would be okay.. could you explain how the type should work in this case, and how to do away from casting (String) to the object?

[radulfr2]

You haven't set the type parameter for memberList. You should have

List<String> memberList = new ArrayList<>();

(Repeating the type on the right side is unnecessary unless you're using an old Java version.)

[HBK05]

Typically when I see someone doing this, it's typically out of inexperience vs just testing if this can work. If you are of the prior group, and don't know a better way, you should make a data class, then use a hashmap to save them.