Preorder Example in Java

public static void printdir (Object dir, int level) {
    for ( int i = 0; i < level; i++ )
        System.out.print("  ");
    if ( ! consp(dir) )
        System.out.println(dir);
    else {  System.out.println(first((Cons) dir));
            while ( rest((Cons) dir) != null ) {
                dir = rest((Cons) dir);
                printdir(first((Cons) dir),
                         level + 1); } } }                

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