Java Reflection - Field.getGenericType() Examples

package com.logicbig.example.field;

import java.lang.reflect.Field;
import java.lang.reflect.Type;
import java.math.BigDecimal;

public class GetGenericTypeExample {
    private int anInt;
    private BigDecimal bigNumber;

    public static void main(String... args) throws NoSuchFieldException {
        Field field = GetGenericTypeExample.class.getDeclaredField("anInt");
        Type type = field.getGenericType();
        printType(field, type);

        Field field2 = GetGenericTypeExample.class.getDeclaredField("bigNumber");
        Type type2 = field2.getGenericType();
        printType(field2, type2);
    }

    private static void printType(Field field, Type type) {
        System.out.printf("Example: %s %s;%n", field.getType().getSimpleName(), field.getName());
        System.out.println("Type class= " + type.getClass());
        System.out.println("Type name= " + type.getTypeName());
    }
}

package com.logicbig.example.field;

import java.lang.reflect.Field;
import java.lang.reflect.Type;
import java.math.BigDecimal;

public class GetGenericTypeExample2 {
    private int numbers[];
    private BigDecimal[] bigNumbers;
    private BigDecimal[][] bigNumbersOfNumbers;

    public static void main(String... args) throws NoSuchFieldException {
        Field field = GetGenericTypeExample2.class.getDeclaredField("numbers");
        Type type = field.getGenericType();
        printType(field, type);

        Field field2 = GetGenericTypeExample2.class.getDeclaredField("bigNumbers");
        Type type2 = field2.getGenericType();
        printType(field2, type2);

        Field field3 = GetGenericTypeExample2.class.getDeclaredField("bigNumbersOfNumbers");
        Type type3 = field3.getGenericType();
        printType(field3, type3);
    }

    private static void printType(Field field, Type type) {
        System.out.printf("Example: %s %s;%n", field.getType().getSimpleName(), field.getName());
        print(1, "Type class= " + type.getClass());
        print(1, "Type name= " + type.getTypeName());
        printArrayComponentType(type, 1);
    }

    private static void printArrayComponentType(Type type, int level) {
        if (type instanceof Class && ((Class) type).isArray()) {
            Class componentType = ((Class) type).getComponentType();
            print(level, "Array component type=" + componentType.getTypeName());
            printArrayComponentType(componentType, level + 1);
        }
    }

    private static void print(int level, String string) {
        System.out.printf("%" + (level * 4 - 3) + "s\u00A6- %s%n", "", string);
    }
}

package com.logicbig.example.field;

import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.Arrays;
import java.util.List;
import java.util.Map;

public class GetGenericTypeExample3 {
    private List<String> aList;
    private Map<String, List<String>> aMap;

    public static void main(String... args) throws NoSuchFieldException {
        System.out.println("Example: List<String> aList;");
        Field field = GetGenericTypeExample3.class.getDeclaredField("aList");
        Type type = field.getGenericType();
        printType(type, 1);

        System.out.println("Example: Map<String, List<String>> aMap;");
        Field field2 = GetGenericTypeExample3.class.getDeclaredField("aMap");
        Type type2 = field2.getGenericType();
        printType(type2, 1);
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            print(level, "The Type is null");
            return;
        }
        print(level, "Type class=" + type.getClass());
        if (type.getClass() != Class.class) {
            print(level, "Type class implementing interfaces=" +
                    Arrays.toString(type.getClass().getInterfaces()));
        }
        print(level, "Type name= " + type.getTypeName());
        printParameterizedType(type, level);
    }

    private static void printParameterizedType(Type type, int level) {
        if (type instanceof ParameterizedType) {
            print(level, "Casting to ParameterizedType");
            ParameterizedType pt = (ParameterizedType) type;
            print(level, "Using ParameterizedType#getOwnerType()");
            Type ownerType = pt.getOwnerType();
            printType(ownerType, level + 1);

            print(level, "Using ParameterizedType#getRawType()");
            Type rawType = pt.getRawType();
            printType(rawType, level + 1);

            print(level, "Using ParameterizedType#getActualTypeArguments()");
            for (Type actualType : pt.getActualTypeArguments()) {
                print(level, "ActualTypeArgument loop");
                printType(actualType, level + 1);
            }
        }
    }

    private static void print(int level, String string) {
        System.out.printf("%" + (level * 4 - 3) + "s\u00A6- %s%n", "", string);
    }
}

package com.logicbig.example.field;

import java.lang.reflect.*;
import java.util.Arrays;
import java.util.List;

public class GetGenericTypeExample4<T> {
    private T t;
    private List<T> list;

    public static void main(String... args) throws NoSuchFieldException {
        System.out.println("Example: T t;");
        Field field = GetGenericTypeExample4.class.getDeclaredField("t");
        Type genericType = field.getGenericType();
        printType(genericType, 1);

        System.out.println("Example: List<T> list;");
        Field field2 = GetGenericTypeExample4.class.getDeclaredField("list");
        Type genericType2 = field2.getGenericType();
        printType(genericType2, 1);
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            print(level, "The Type is null");
            return;
        }
        print(level, "Type class=" + type.getClass());
        if (type.getClass() != Class.class) {
            print(level, "Type class implementing interfaces=" +
                    Arrays.toString(type.getClass().getInterfaces()));
        }
        print(level, "Type name= " + type.getTypeName());
        printTypeVariable(type, level);
        printParameterizedType(type, level);
    }

    private static void printTypeVariable(Type type, int level) {
        if (type instanceof TypeVariable) {
            print(level, "Casting to TypeVariable");
            TypeVariable typeVariable = (TypeVariable) type;
            print(level, "TypeVariable#getName()= " + typeVariable.getName());
            GenericDeclaration genericDeclaration = typeVariable.getGenericDeclaration();
            print(level, "TypeVariable#getGenericDeclaration()= " + genericDeclaration);
            printGenericDeclaration(level, genericDeclaration);
        }
    }

    private static void printGenericDeclaration(int level, GenericDeclaration genericDeclaration) {
        print(level, "GenericDeclaration#getTypeParameters()= " +
                Arrays.toString(genericDeclaration.getTypeParameters()));
    }

    private static void printParameterizedType(Type type, int level) {
        if (type instanceof ParameterizedType) {
            print(level, "Casting to ParameterizedType");
            ParameterizedType pt = (ParameterizedType) type;
            print(level, "Using ParameterizedType#getOwnerType()");
            Type ownerType = pt.getOwnerType();
            printType(ownerType, level + 1);

            print(level, "Using ParameterizedType#getRawType()");
            Type rawType = pt.getRawType();
            printType(rawType, level + 1);

            print(level, "Using ParameterizedType#getActualTypeArguments()");
            for (Type actualType : pt.getActualTypeArguments()) {
                print(level, "ActualTypeArgument loop");
                printType(actualType, level + 1);
            }
        }
    }

    private static void print(int level, String string) {
        System.out.printf("%" + (level * 4 - 3) + "s\u00A6- %s%n", "", string);
    }

}

package com.logicbig.example.field;

import java.lang.reflect.*;
import java.util.Arrays;
import java.util.List;

public class GetGenericTypeExample5<T> {
    private T[] ts;
    private List<T[]> tsList;

    public static void main(String... args) throws NoSuchFieldException {
        System.out.println("Example: T[] ts;");
        Field field = GetGenericTypeExample5.class.getDeclaredField("ts");
        Type genericType = field.getGenericType();
        printType(genericType, 1);

        System.out.println("Example: List<T[]> tsList;");
        Field field2 = GetGenericTypeExample5.class.getDeclaredField("tsList");
        Type genericType2 = field2.getGenericType();
        printType(genericType2, 1);
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            print(level, "The Type is null");
            return;
        }
        print(level, "Type class=" + type.getClass());
        if (type.getClass() != Class.class) {
            print(level, "Type class implementing interfaces=" +
                    Arrays.toString(type.getClass().getInterfaces()));
        }
        print(level, "Type name= " + type.getTypeName());
        printTypeVariable(type, level);
        printParameterizedType(type, level);
        printGenericArrayType(type, level);
    }

    private static void printGenericArrayType(Type type, int level) {
        if(type instanceof GenericArrayType){
            print(level, "Casting to GenericArrayType");
            GenericArrayType genericArrayType = (GenericArrayType) type;
            print(level, "Using GenericArrayType#getGenericComponentType()" );
            Type genericComponentType = genericArrayType.getGenericComponentType();
            printType( genericComponentType, level+1);
        }
    }

    private static void printTypeVariable(Type type, int level) {
        if (type instanceof TypeVariable) {
            print(level, "Casting to TypeVariable");
            TypeVariable typeVariable = (TypeVariable) type;
            print(level, "TypeVariable#getName()= " + typeVariable.getName());
            GenericDeclaration genericDeclaration = typeVariable.getGenericDeclaration();
            print(level, "TypeVariable#getGenericDeclaration()= " + genericDeclaration);
            printGenericDeclaration(level, genericDeclaration);
        }
    }

    private static void printGenericDeclaration(int level, GenericDeclaration genericDeclaration) {
        print(level, "GenericDeclaration#getTypeParameters()= " +
                Arrays.toString(genericDeclaration.getTypeParameters()));
    }

    private static void printParameterizedType(Type type, int level) {
        if (type instanceof ParameterizedType) {
            print(level, "Casting to ParameterizedType");
            ParameterizedType pt = (ParameterizedType) type;
            print(level, "Using ParameterizedType#getOwnerType()");
            Type ownerType = pt.getOwnerType();
            printType(ownerType, level + 1);

            print(level, "Using ParameterizedType#getRawType()");
            Type rawType = pt.getRawType();
            printType(rawType, level + 1);

            print(level, "Using ParameterizedType#getActualTypeArguments()");
            for (Type actualType : pt.getActualTypeArguments()) {
                print(level, "ActualTypeArgument loop");
                printType(actualType, level + 1);
            }
        }
    }

    private static void print(int level, String string) {
        System.out.printf("%" + (level * 4 - 3) + "s\u00A6- %s%n", "", string);
    }
} 

package com.logicbig.example.field;

import javax.swing.*;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.WildcardType;
import java.util.Arrays;
import java.util.List;
import java.util.Map;

public class GetGenericTypeExample6 {
    private List<?> list;
    private Map<? extends Number, ? super JFormattedTextField> map;

    public static void main(String... args) throws NoSuchFieldException {
        System.out.println("Example: List<?> list;");
        Field field = GetGenericTypeExample6.class.getDeclaredField("list");
        Type genericType = field.getGenericType();
        printType(genericType, 1);

        System.out.println("Example: Map<? extends Number, ? super JFormattedTextField> map");
        Field field2 = GetGenericTypeExample6.class.getDeclaredField("map");
        Type genericType2 = field2.getGenericType();
        printType(genericType2, 1);
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            print(level, "The Type is null");
            return;
        }
        print(level, "Type class=" + type.getClass());
        if (type.getClass() != Class.class) {
            print(level, "Type class implementing interfaces=" +
                    Arrays.toString(type.getClass().getInterfaces()));
        }
        print(level, "Type name= " + type.getTypeName());
        printWildcardType(type, level);
        printParameterizedType(type, level);
    }

    private static void printParameterizedType(Type type, int level) {
        if (type instanceof ParameterizedType) {
            print(level, "Casting to ParameterizedType");
            ParameterizedType pt = (ParameterizedType) type;
            print(level, "Using ParameterizedType#getOwnerType()");
            Type ownerType = pt.getOwnerType();
            printType(ownerType, level + 1);

            print(level, "Using ParameterizedType#getRawType()");
            Type rawType = pt.getRawType();
            printType(rawType, level + 1);

            print(level, "Using ParameterizedType#getActualTypeArguments()");
            for (Type actualType : pt.getActualTypeArguments()) {
                print(level, "ActualTypeArgument loop");
                printType(actualType, level + 1);
            }
        }
    }

    private static void printWildcardType(Type type, int level) {
        if (type instanceof WildcardType) {
            print(level, "Casting to WildcardType");
            WildcardType wildcardType = (WildcardType) type;
            print(level, "Using WildcardType#getLowerBounds()");
            if (wildcardType.getLowerBounds().length > 0) {
                for (Type lowerBoundType : wildcardType.getLowerBounds()) {
                    print(level, "lowerBoundType loop");
                    printType(lowerBoundType, level + 1);
                }
            } else {
                print(level, "No lowerBoundType found");
            }
            if (wildcardType.getUpperBounds().length > 0) {
                print(level, "Using WildcardType#getUpperBounds()");
                for (Type upperBoundType : wildcardType.getUpperBounds()) {
                    print(level, "upperBoundType loop");
                    printType(upperBoundType, level + 1);
                }
            } else {
                print(level, "No upperBoundType found");
            }
        }
    }

    private static void print(int level, String string) {
        System.out.printf("%" + (level * 4 - 3) + "s\u00A6- %s%n", "", string);
    }
}