toString()

Here are the completed methods along with a not-quite complete toString() method.

// Forest.java
//
public class Forest
{
  // instance variables
  private Tree tree0=null, tree1=null, tree2=null, tree3=null;
   
  // default constructor supplied automatically
  
  // methods
  public void setTree( int treeNum, Tree tree )
  {
    if      ( treeNum == 0 )  tree0 = tree;
    else if ( treeNum == 1  ) tree1 = tree;
    else if ( treeNum == 2  ) tree2 = tree;
    else if ( treeNum == 3  ) tree3 = tree;
  }
  
  public Tree getTree( int treeNum )
  {
    if      ( treeNum == 0  ) return tree0;
    else if ( treeNum == 1  ) return tree1;
    else if ( treeNum == 2  ) return tree2;
    else if ( treeNum == 3  ) return tree3;
    
    return null;
  }
  
  // build a string
  public String toString()
  {
        if (  ) 
      return "No Trees in Forest";
    
    String str = "Forest:\n"; 
    if ( tree0 != null ) str += "Tree 0: " + tree0.toString() + "\n";
   
    return str;
    
   
  }
}