MAP/LIST를 빌드하기 위한 Java의 빌더 모드에 대한 자세한 소개

import java.util.HashMap;
import java.util.Map;
 
public class MapBuilder<T> {
  
 public Builder<T> b;
  
 public MapBuilder(Builder<T> b){
  this.b = b;
 }
  
 public Map<String,T> map(){
  return b.map;
 }
  
 public T get(String key){
  return b.map.get(key);
 }
 
 public static class Builder<T>{
   
  public Map<String, T> map;
   
  public Builder(){
   map = new HashMap<String, T>();
  }
   
  public Builder<T> map(String key, T value){
   map.put(key, value);
   return this;
  }
   
   
  public MapBuilder<T> build(){
   return new MapBuilder<T>(this);
  }
 }
  
 public static void main(String[] args) {
  MapBuilder<String> build = new MapBuilder.Builder<String>().map("a", "b").build();
  System.out.println(build.get("a"));
 }
  
}

public class ListBuilder<T> {
  
 public Builder<T> b;
  
 public ListBuilder(Builder<T> b){
  this.b = b;
 }
  
 public List<T> list(){
  return b.list;
 }
  
 public T get(int index){
  return b.list.get(index);
 }
 
 public static class Builder<T>{
   
  public List<T> list;
   
  public Builder(){
   list = new ArrayList<T>();
  }
  public Builder<T> add(T value){
   list.add(value);
   return this;
  }
  public ListBuilder<T> build(){
   return new ListBuilder<T>(this);
  }
 }
  
 public static void main(String[] args) {
  ListBuilder<String> build = new ListBuilder.Builder<String>().add("a").add("b").build();
  System.out.println(build.get(0));
 }
}