Map without using an array in java

I wrote an article like this the other day.

I want to get rid of the over-nested ()

I wrote here

// using custom object
const applier = (val)=>{
  const  o={
    value : val,
    apply : (unary)=>{ o.value=unary(o.value); return o; }
  return o;

Let's convert this to java today.

public class Applier<T> {
  private T value;
  public Applier(T value) {
    this.value = value;
  // import java.util.function.Function;
  public <R> Applier<R> apply(Function<? super T, ? extends R> appliable){
    return new Applier<R>(appliable.apply(this.value));
  public T get() { return this.value; }

That's right if you use the java.util.function.Function interface.

It is this one line that will be the key.

  public <R> Applier<R> apply(Function<? super T, ? extends R> appliable){

Because of this, it is possible to process even if the input and output have different types.

For example

  new Applier<String>("0001")
    .apply(v->String.format("%04d", v))

It can be used like this.


    return new Applier<R>(appliable.apply(this.value));

This one line feels strange, so I want to write it like this.

public class Applier<T> {
  private T value;
  public Applier(T value) {
    this.value = value;
  public <R> Applier<R> apply(Appliable<? super T, ? extends R> appliable){
    return new Applier<R>(appliable.applyTo(this.value));
  public T get() { return this.value; }
  public static interface Appliable<T, R> {
    public R applyTo(T value);

The public static interface is used to prevent namespace pollution.

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