import java.util.function.BiFunction; public class Main { // an example tree builder // adjust to your liking public static BinTree makeTree() { /* Example tree A / \ B C / \ \ A C D */ BinTree rootNode = new BinTree<>('A'); rootNode.setLeftBranch(new BinTree<>('B', new BinTree<>('A'), new BinTree<>('C'))); rootNode.setRightBranch(new BinTree<>('C', null, new BinTree<>('D'))); return rootNode; } // driver routine, // here: count number of 'A's in the tree public static void main(String[] args) { var rootNode = makeTree(); int count = InOrderBiFunction.apply( /* init */ 0, /* tree root */ rootNode, /* operation */ (_cnt, _payload) -> _payload == 'A' ? _cnt + 1 : _cnt ); System.out.println(count); } } // A class to operate on a BinTree using a BiFunction // The algorithm is a recursive in-order tree walk public class InOrderBiFunction { public static R apply(R init, BinTree tree, BiFunction op) { if(tree != null) { R v = apply(init, tree.getLeftBranch(), op); v = op.apply(v, tree.getPayload()); return apply(v, tree.getRightBranch(), op); } else { return init; } } } // a pure data class // there are no fancy methods in here, just getters and setters public final class BinTree { private T payload; private BinTree leftBranch; private BinTree rightBranch; public BinTree(T payload) { this.payload = payload; this.leftBranch = null; this.rightBranch = null; } public BinTree(T payload, BinTree leftBranch, BinTree rightBranch) { this.payload = payload; this.leftBranch = leftBranch; this.rightBranch = rightBranch; } public T getPayload() { return payload; } public void setPayload(U payload) { this.payload = payload; } public BinTree getLeftBranch() { return leftBranch; } public void setLeftBranch(BinTree leftBranch) { this.leftBranch = leftBranch; } public BinTree getRightBranch() { return rightBranch; } public void setRightBranch(BinTree rightBranch) { this.rightBranch = rightBranch; } }

BinTree with operation classes