Cannot Instantiate Type in generics

Question

I have this class

public class Tree {

    //List of branches for this tree
    private List> branch = new ArrayList<         


        

Answer 1

Wildcards ? cannot be used when creating new instances. You should change your code to something like that

import java.util.ArrayList;
import java.util.List;

public class Test1 {
  public static void main(String[] args){
    Tree num2 = new Tree(2);
    num2.addBranch(new Tree(1));
    Tree num3 = (Tree) num2.getBranch(0);
    System.out.println(num3);
  }
}

class Tree {

  //List of branches for this tree
  private List> branch = new ArrayList>();
  public Tree(T t){ this.t = t; }
  public void addBranch(Tree src){ branch.add((Tree) src); }
  public Tree getBranch(int branchNum){
    return (Tree) branch.get(branchNum);
  }

  public String toString(){
    return String.valueOf(t);
  }

  private T t;

}