Java Performance - Not allocating strings for Constants (#246)

This change also contributes to the improvement of java performance.
Avoid creating constants as strings everytime we evaluating configs.

**This is the last PR on this Improvment**

Author: weihao-statsig

src/main/kotlin/com/statsig/sdk/ClientInitializeFormatter.kt

@@ -45,7 +45,7 @@ internal data class ClientConfig(
 
 internal class ClientInitializeFormatter(
     private val specStore: SpecStore,
-    private val evalFun: (user: StatsigUser, config: APIConfig?) -> ConfigEvaluation,
+    private val evalFun: (user: StatsigUser, config: APIConfig?, endResult: ConfigEvaluation) -> Unit,
     private val user: StatsigUser,
     private val hash: HashAlgo = HashAlgo.SHA256,
     private val clientSDKKey: String? = null,
@@ -132,7 +132,8 @@ internal class ClientInitializeFormatter(
 
         if (delegate != null && delegate != "") {
             val delegateSpec = specStore.getConfig(delegate)
-            val delegateResult = evalFun(user, delegateSpec)
+            var delegateResult = ConfigEvaluation()
+            evalFun(user, delegateSpec, delegateResult)
             if (delegateSpec != null) {
                 result.allocatedExperimentName = hashName(delegate)
                 result.isUserInExperiment = delegateResult.isExperimentGroup
@@ -154,7 +155,8 @@ internal class ClientInitializeFormatter(
             return null
         }
 
-        val evalResult = evalFun(user, configSpec)
+        val evalResult = ConfigEvaluation()
+        evalFun(user, configSpec, evalResult)
         val hashedName = hashName(configName)
         val result = ClientConfig(
             hashedName,

src/main/kotlin/com/statsig/sdk/Const.kt

@@ -0,0 +1,68 @@
+package com.statsig.sdk
+
+object Const {
+    const val EMPTY_STR: String = ""
+    const val ZERO: String = "0"
+
+    const val GT: String = "gt"
+    const val GTE: String = "gte"
+    const val LT: String = "lt"
+    const val LTE: String = "lte"
+    const val VERSION_GT: String = "version_gt"
+    const val VERSION_GTE: String = "version_gte"
+    const val VERSION_LT: String = "version_lt"
+    const val VERSION_LTE: String = "version_lte"
+    const val VERSION_EQ: String = "version_eq"
+    const val VERSION_NEQ: String = "version_neq"
+    const val ANY: String = "any"
+    const val ANY_CASE_SENSITIVE: String = "any_case_sensitive"
+    const val NONE_CASE_SENSITIVE: String = "none_case_sensitive"
+    const val STR_STARTS_WITH_ANY: String = "str_starts_with_any"
+    const val STR_ENDS_WITH_ANY: String = "str_ends_with_any"
+    const val STR_CONTAINS_ANY: String = "str_contains_any"
+    const val STR_CONTAINS_NONE: String = "str_contains_none"
+    const val STR_MATCHES: String = "str_matches"
+    const val EQ: String = "eq"
+    const val NEQ: String = "neq"
+    const val BEFORE: String = "before"
+    const val AFTER: String = "after"
+    const val ON: String = "on"
+    const val IN_SEGMENT_LIST: String = "in_segment_list"
+    const val NOT_IN_SEGMENT_LIST: String = "not_in_segment_list"
+
+    const val APP_VERSION: String = "app_version"
+    const val APPVERSION: String = "appversion"
+    const val BROWSER_NAME: String = "browser_name"
+    const val BROWSER_VERSION: String = "browser_version"
+    const val BROWSERNAME: String = "browsername"
+    const val BROWSERVERSION: String = "browserversion"
+    const val CML_SHA_256: String = "SHA-256"
+    const val COUNTRY: String = "country"
+    const val DEFAULT: String = "default"
+    const val DISABLED: String = "disabled"
+    const val EMAIL: String = "email"
+    const val IP: String = "ip"
+    const val IPADDRESS: String = "ipaddress"
+    const val IP_ADDRESS: String = "ip_address"
+    const val LOCALE: String = "locale"
+    const val NONE: String = "none"
+    const val OS_NAME: String = "os_name"
+    const val OS_VERSION: String = "os_version"
+    const val OSNAME: String = "osname"
+    const val OSVERSION: String = "osversion"
+    const val USER_AGENT: String = "user_agent"
+    const val USER_ID: String = "user_id"
+    const val USERAGENT: String = "useragent"
+    const val USERID: String = "userid"
+
+    const val PUBLIC: String = "public"
+    const val FAIL_GATE: String = "fail_gate"
+    const val PASS_GATE: String = "pass_gate"
+    const val IP_BASED: String = "ip_based"
+    const val UA_BASED: String = "ua_based"
+    const val USER_FIELD: String = "user_field"
+    const val CURRENT_TIME: String = "current_time"
+    const val ENVIRONMENT_FIELD: String = "environment_field"
+    const val USER_BUCKET: String = "user_bucket"
+    const val UNIT_ID: String = "unit_id"
+}