StringUniquenessChecker

import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.function.Function;

/**
 *
 * The class purpose is to optimize memory usage checking for duplicates in a
 * list or stream of strings
 *
 */
public class StringUniquenessChecker {

    private Map<Integer, Map<String, Integer>> stringUsage = new HashMap<>();
    private Set<Integer> hashCodes = new HashSet<>();

    public void doAction1(List<String> list, Function<String,Void> func) {
        for (int i = 0; i< list.size(); i++) {
            String string = list.get(i);
            int hashCode = string.hashCode();

            if (!hashCodes.contains(hashCode)) {
                stringUsage.put(hashCode, null);
                func.apply(string);
            } else {
                if (!stringUsage.containsKey(hashCode)) {
                    Map<String, Integer> stringCountMap = new HashMap<>();
                    stringCountMap.put(string, 0);
                    stringUsage.putIfAbsent(hashCode, stringCountMap);
                    func.apply(string);
                } else {
                    Map<String, Integer> stringCountMap = stringUsage.get(hashCode);
                    if (stringCountMap != null) {
                        Integer count = stringCountMap.get(string);
                        if (count == null) {
                            stringCountMap.put(string, 1);
                            func.apply(string);
                        } else {
                            stringCountMap.put(string, count + 1);
                            func.apply(string);
                        }
                        stringUsage.put(hashCode, stringCountMap);

                    } else {
                        stringCountMap = new HashMap<>();
                        stringCountMap.put(string, 1);
                        stringUsage.put(hashCode, stringCountMap);

                    }

                }
            }

            hashCodes.add(hashCode);
        }

    }

    public void doAction(Function<String,Void> func) {

        for (int i = 0; i< 1000; i++) {
            String string = StringProvider.provide();
            int hashCode = string.hashCode();

            if (!hashCodes.contains(hashCode)) {
                stringUsage.put(hashCode, null);
            } else {
                if (!stringUsage.containsKey(hashCode)) {
                    Map<String, Integer> stringCountMap = new HashMap<>();
                    stringCountMap.put(string, 0);
                    stringUsage.putIfAbsent(hashCode, stringCountMap);
                } else {
                    Map<String, Integer> stringCountMap = stringUsage.get(hashCode);
                    if (stringCountMap != null) {
                        Integer count = stringCountMap.get(string);
                        if (count == null) {
                            stringCountMap.put(string, 1);
                        } else {
                            stringCountMap.put(string, count + 1);
                        }
                        stringUsage.put(hashCode, stringCountMap);
                    } else {
                        stringCountMap = new HashMap<>();
                        stringCountMap.put(string, 1);
                        stringUsage.put(hashCode, stringCountMap);
                    }

                }
            }

            hashCodes.add(hashCode);
        }

        for (int i = 0; i< 1000; i++) {
            String string = StringProvider.provide();
            int hashCode = string.hashCode();

            Map<String, Integer> stringCountMap = stringUsage.get(hashCode);
            if (stringCountMap == null) {
                func.apply(string);
            } else {

                Integer countOfString = stringCountMap.get(string);
                if (countOfString == null || countOfString == 1) {
                    func.apply(string);
                }
                if (countOfString != null) {
                    stringCountMap.put(string, countOfString - 1);
                }
            }
        }

    }

}