Enum-Allocation-Example.java

package info.gamlor.blog;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

enum TypeInfo {
    UNKNOWN(0),
    INT(1),
    STRING(2);

    private final int id;

    TypeInfo(int id) {
        this.id = id;
    }

    public static TypeInfo findType(int type){
        for (TypeInfo t : values()){
            if(t.id == type){
                return t;
            }
        }
        return UNKNOWN;
    }
}

public class Main {
    private static Random rnd = new Random();

    public static void main(String[] args) throws Exception {
        List<TypeInfo> parsedData = new ArrayList<>();
        for (int i = 0; i < 1000000000; i++) {
            int idParsedFromWire = readTypeIdFromData(rnd);

            TypeInfo type = TypeInfo.findType(idParsedFromWire);

            // Pretend we use the type for the exampe
            parsedData.add(type);
            consumeData(parsedData);
        }
        System.out.println(parsedData.size());
    }

    private static void consumeData(List<TypeInfo> parsedData) {
        // Parsed data is consumed
        if(rnd.nextBoolean()){
            parsedData.clear();
        }
    }

    private static int readTypeIdFromData(Random rnd) throws InterruptedException {
        // Data comes from the wire....let's run this example a bit slower
        int idParsedFromWire = rnd.nextInt(16);
        Thread.yield();
        return idParsedFromWire;
    }
}

Fix.java

// Enum.values() does a defensive copy and allocates an array on each call
// To avoid that allocation, we call values() only once
private static final TypeInfo[] ALL_VALUES = values();

public static TypeInfo findType(int type){
    for (TypeInfo t : ALL_VALUES){
        if(t.id == type){
            return t;
        }
    }
    return UNKNOWN;
}