java.lang.AssertionError: illegal type variable reference

i use gson 2.8.5 in android project，run app with proguard on real Android Phone. when execute code Type listType = new TypeToken<List<T>>() {}.getType()，then crash:

 java.lang.AssertionError: illegal type variable reference
        at libcore.reflect.TypeVariableImpl.resolve(TypeVariableImpl.java:111)
        at libcore.reflect.TypeVariableImpl.getGenericDeclaration(TypeVariableImpl.java:125)
        at libcore.reflect.TypeVariableImpl.hashCode(TypeVariableImpl.java:47)
        at java.util.Arrays.hashCode(Arrays.java:4153)
        at com.google.gson.internal.$Gson$Types$ParameterizedTypeImpl.hashCode($Gson$Types.java:502)
        at com.google.gson.reflect.TypeToken.<init>(TypeToken.java:64)
......

i have add these code in proguard.pro:

-keepattributes Exceptions
-keepattributes InnerClasses
-keepattributes Signature
-keepattributes Deprecated
-keepattributes SourceFile
-keepattributes LineNumberTable
-keepattributes *Annotation*
-keepattributes EnclosingMethod

# Gson specific classes
-keep class sun.** { *; }
#-keep class com.google.gson.stream.** { *; }

# Prevent proguard from stripping interface information from TypeAdapterFactory,
# JsonSerializer, JsonDeserializer instances (so they can be used in @JsonAdapter)
-keep class * implements com.google.gson.TypeAdapterFactory
-keep class * implements com.google.gson.JsonSerializer
-keep class * implements com.google.gson.JsonDeserializer

[kkmike999]

@lyubomyr-shaydariv maybe some other config cause this error. i config build.gradle

android {
 buildTypes{
    alpha {
            minifyEnabled true
            zipAlignEnabled true
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro', 'proguard-rules-2.0.pro'
            signingConfig signingConfigs.releaseConfig
            multiDexKeepProguard file('keep_in_main_dex.pro')
            debuggable = false

            // matchingFallbacks属性来设置回退策略（必填，http://codezjx.com/2017/11/23/gradle-plugin-3-0-0-migration/)
            matchingFallbacks = ['release']
        }
    }
}

the problem solve. But when config debuggable = ture, the error occur T_T.

[lyubomyr-shaydariv]

@rosuH No need to have it such complex. You can simply create a method like this:

public static <T> List<T> fromJsonToList(final String json, final Class<T> elementClass) {
	return gson.fromJson(json, TypeToken.getParameterized(List.class, elementClass).getType());
}

that will do the job. I’d only recommend this method if you provide the element types dynamically, not statically (also note that gson can be re-used, no need to new it). However, I believe you only need something like this:

private static final TypeToken<List<Short>> listOfShorts = new TypeToken<List<Short>>() {};
private static final TypeToken<List<Float>> listOfFloats = new TypeToken<List<Float>>() {};

public static void main(final String... args) {
	final String json = "[1,2,3,4,5,6]";
	System.out.println(gson.<List<Short>>fromJson(json, listOfShorts.getType()));
	System.out.println(gson.<List<Float>>fromJson(json, listOfFloats.getType()));
}

that would produce [1, 2, 3, 4, 5, 6] and [1.0, 2.0, 3.0, 4.0, 5.0, 6.0] respectively. It is a little more verbose, but you don’t need to implement custom methods, and you can reuse type tokens too.