Java Reflection - Method.getGenericReturnType() Examples

Class:

java.lang.reflect.Method

Method:

public Type getGenericReturnType()

Returns a Type object that represents the formal return type of the method represented by this Method object.

Examples

package com.logicbig.example.method;

import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.util.Arrays;
import java.util.Objects;

public class GetGenericReturnTypeExample<N extends Number> {

    public N process() {return null;}

    public static void main(String... args) throws NoSuchMethodException {
        Method m = GetGenericReturnTypeExample.class.getDeclaredMethod("process");
        Type t = m.getGenericReturnType();
        printType(t, 1);
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            return;
        }
        print(level, "type: " + Objects.toString(type));
        if (type instanceof TypeVariable) {
            print(level, "type is an instance of TypeVariable");
            printTypeVariable((TypeVariable) type, level + 1);
        } else if (type instanceof Class) {
            print(level, "type is an instance of Class");
            print(level, "Class Name: " + ((Class) type).getName());
        } else {
            throw new RuntimeException();
        }
    }

    private static void printTypeVariable(TypeVariable type, int level) {
        print(level, "TypeVariable#getName(): " + type.getName());
        Type[] bounds = type.getBounds();
        print(level, "TypeVariable#getBounds(): " + Arrays.toString(bounds));
        for (Type bound : bounds) {
            print(level, "TypeVariable#bound: " + bound);
            printType(bound, level + 1);
        }
    }

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

Output

 ¦- type: N
 ¦- type is an instance of TypeVariable
     ¦- TypeVariable#getName(): N
     ¦- TypeVariable#getBounds(): [class java.lang.Number]
     ¦- TypeVariable#bound: class java.lang.Number
         ¦- type: class java.lang.Number
         ¦- type is an instance of Class
         ¦- Class Name: java.lang.Number

package com.logicbig.example.method;

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

public class GetGenericReturnTypeExample2<N extends Number> {

    public N[] process() {return null;}

    public static void main(String... args) throws NoSuchMethodException {
        Method m = GetGenericReturnTypeExample2.class.getDeclaredMethod("process");
        Type type = m.getGenericReturnType();
        printType(type, 1);
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            return;
        }
        print(level, "type: " + Objects.toString(type));
        if (type instanceof TypeVariable) {
            print(level, "type is an instance of TypeVariable");
            printTypeVariable((TypeVariable) type, level + 1);
        } else if (type instanceof Class) {
            print(level, "type is an instance of Class");
            print(level, "Class Name: " + ((Class) type).getName());
        } else if (type instanceof GenericArrayType) {
            print(level, "type is an instance of GenericArrayType");
            printGenericArrayType((GenericArrayType) type, level + 1);
        } else {
            throw new RuntimeException();
        }
    }

    private static void printGenericArrayType(GenericArrayType type, int level) {
        Type componentType = type.getGenericComponentType();
        print(level, "GenericArrayType#getGenericComponentType(): " + componentType);
        printType(componentType, level + 1);
    }

    private static void printTypeVariable(TypeVariable type, int level) {
        print(level, "TypeVariable#getName(): " + type.getName());
        Type[] bounds = type.getBounds();
        print(level, "TypeVariable#getBounds(): " + Arrays.toString(bounds));
        for (Type bound : bounds) {
            print(level, "TypeVariable#bound: " + bound);
            printType(bound, level + 1);
        }
    }

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

Output

 ¦- type: N[]
 ¦- type is an instance of GenericArrayType
     ¦- GenericArrayType#getGenericComponentType(): N
         ¦- type: N
         ¦- type is an instance of TypeVariable
             ¦- TypeVariable#getName(): N
             ¦- TypeVariable#getBounds(): [class java.lang.Number]
             ¦- TypeVariable#bound: class java.lang.Number
                 ¦- type: class java.lang.Number
                 ¦- type is an instance of Class
                 ¦- Class Name: java.lang.Number

package com.logicbig.example.method;

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

public class GetGenericReturnTypeExample3<N extends Number> {

    public List<N> process() {return null;}

    public static void main(String... args) throws NoSuchMethodException {
        Method m = GetGenericReturnTypeExample3.class.getDeclaredMethod("process");
        Type type = m.getGenericReturnType();
        printType(type, 1);
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            return;
        }
        print(level, "type: " + Objects.toString(type));
        if (type instanceof TypeVariable) {
            print(level, "type is an instance of TypeVariable");
            printTypeVariable((TypeVariable) type, level + 1);
        } else if (type instanceof Class) {
            print(level, "type is an instance of Class");
            print(level, "Class Name: " + ((Class) type).getName());
        } else if (type instanceof ParameterizedType) {
            print(level, "type is an instance of ParameterizedType");
            printParameterizeType((ParameterizedType) type, level + 1);
        } else {
            throw new RuntimeException();
        }
    }

    private static void printParameterizeType(ParameterizedType type, int level) {
        Type ownerType = type.getOwnerType();
        print(level, "ParameterizedType#getOwnerType(): " + ownerType);
        printType(ownerType, level + 1);
        Type rawType = type.getRawType();
        print(level, "ParameterizedType#getRawType(): " + rawType);
        printType(rawType, level + 1);
        Type[] types = type.getActualTypeArguments();
        print(level, "ParameterizedType#getActualTypeArguments(): " + Arrays.toString(types));
        for (Type type1 : types) {
            print(level, "ParameterizedType#actualTypeArgument: " + type1);
            printType(type1, level + 1);
        }
    }

    private static void printTypeVariable(TypeVariable type, int level) {
        print(level, "TypeVariable#getName(): " + type.getName());
        Type[] bounds = type.getBounds();
        print(level, "TypeVariable#getBounds(): " + Arrays.toString(bounds));
        for (Type bound : bounds) {
            print(level, "TypeVariable#bound: " + bound);
            printType(bound, level + 1);
        }
    }

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

Output

 ¦- type: java.util.List<N>
 ¦- type is an instance of ParameterizedType
     ¦- ParameterizedType#getOwnerType(): null
     ¦- ParameterizedType#getRawType(): interface java.util.List
         ¦- type: interface java.util.List
         ¦- type is an instance of Class
         ¦- Class Name: java.util.List
     ¦- ParameterizedType#getActualTypeArguments(): [N]
     ¦- ParameterizedType#actualTypeArgument: N
         ¦- type: N
         ¦- type is an instance of TypeVariable
             ¦- TypeVariable#getName(): N
             ¦- TypeVariable#getBounds(): [class java.lang.Number]
             ¦- TypeVariable#bound: class java.lang.Number
                 ¦- type: class java.lang.Number
                 ¦- type is an instance of Class
                 ¦- Class Name: java.lang.Number

package com.logicbig.example.method;

import javax.swing.*;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.WildcardType;
import java.util.Arrays;
import java.util.Map;
import java.util.Objects;

public class GetGenericReturnTypeExample4 {
    Map<? extends Number, ? super JFormattedTextField> process() {return null;}

    public static void main(String... args) throws NoSuchMethodException {
        Method m = GetGenericReturnTypeExample4.class.getDeclaredMethod("process");
        Type type = m.getGenericReturnType();
        printType(type, 1);
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            return;
        }
        print(level, "type: " + Objects.toString(type));
        if (type instanceof Class) {
            print(level, "type is an instance of Class");
            print(level, "Class Name: " + ((Class) type).getName());
        } else if (type instanceof ParameterizedType) {
            print(level, "type is an instance of ParameterizedType");
            printParameterizeType((ParameterizedType) type, level + 1);
        } else if (type instanceof WildcardType) {
            print(level, "type is an instance of WildcardType");
            printWildcardType((WildcardType) type, level + 1);
        } else {
            throw new RuntimeException();
        }
    }

    private static void printWildcardType(WildcardType type, int level) {
        Type[] lowerBounds = type.getLowerBounds();
        print(level, "WildcardType#getLowerBounds(): " + Arrays.toString(lowerBounds));
        for (Type lowerBound : lowerBounds) {
            print(level, "WildcardType#lowerBound: " + lowerBound);
            printType(lowerBound, level + 1);
        }
        Type[] upperBounds = type.getUpperBounds();
        print(level, "WildcardType#getUpperBounds(): " + Arrays.toString(upperBounds));
        for (Type upperBound : upperBounds) {
            print(level, "WildcardType#upperBound: " + upperBound);
            printType(upperBound, level + 1);
        }
    }

    private static void printParameterizeType(ParameterizedType type, int level) {
        Type ownerType = type.getOwnerType();
        print(level, "ParameterizedType#getOwnerType(): " + ownerType);
        printType(ownerType, level + 1);
        Type rawType = type.getRawType();
        print(level, "ParameterizedType#getRawType(): " + rawType);
        printType(rawType, level + 1);
        Type[] types = type.getActualTypeArguments();
        print(level, "ParameterizedType#getActualTypeArguments(): " + Arrays.toString(types));
        for (Type type1 : types) {
            print(level, "ParameterizedType#actualTypeArgument: " + type1);
            printType(type1, level + 1);
        }
    }

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

Output

 ¦- type: java.util.Map<? extends java.lang.Number, ? super javax.swing.JFormattedTextField>
 ¦- type is an instance of ParameterizedType
     ¦- ParameterizedType#getOwnerType(): null
     ¦- ParameterizedType#getRawType(): interface java.util.Map
         ¦- type: interface java.util.Map
         ¦- type is an instance of Class
         ¦- Class Name: java.util.Map
     ¦- ParameterizedType#getActualTypeArguments(): [? extends java.lang.Number, ? super javax.swing.JFormattedTextField]
     ¦- ParameterizedType#actualTypeArgument: ? extends java.lang.Number
         ¦- type: ? extends java.lang.Number
         ¦- type is an instance of WildcardType
             ¦- WildcardType#getLowerBounds(): []
             ¦- WildcardType#getUpperBounds(): [class java.lang.Number]
             ¦- WildcardType#upperBound: class java.lang.Number
                 ¦- type: class java.lang.Number
                 ¦- type is an instance of Class
                 ¦- Class Name: java.lang.Number
     ¦- ParameterizedType#actualTypeArgument: ? super javax.swing.JFormattedTextField
         ¦- type: ? super javax.swing.JFormattedTextField
         ¦- type is an instance of WildcardType
             ¦- WildcardType#getLowerBounds(): [class javax.swing.JFormattedTextField]
             ¦- WildcardType#lowerBound: class javax.swing.JFormattedTextField
                 ¦- type: class javax.swing.JFormattedTextField
                 ¦- type is an instance of Class
                 ¦- Class Name: javax.swing.JFormattedTextField
             ¦- WildcardType#getUpperBounds(): [class java.lang.Object]
             ¦- WildcardType#upperBound: class java.lang.Object
                 ¦- type: class java.lang.Object
                 ¦- type is an instance of Class
                 ¦- Class Name: java.lang.Object

package com.logicbig.example.method;

import java.lang.reflect.Method;
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.Objects;

public class GetGenericReturnTypeExample5 {
    List<?> process() {return null;}

    public static void main(String... args) throws NoSuchMethodException {
        Method m = GetGenericReturnTypeExample5.class.getDeclaredMethod("process");
        Type type = m.getGenericReturnType();
        printType(type, 1);
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            return;
        }
        print(level, "type: " + Objects.toString(type));
        if (type instanceof Class) {
            print(level, "type is an instance of Class");
            print(level, "Class Name: " + ((Class) type).getName());
        } else if (type instanceof ParameterizedType) {
            print(level, "type is an instance of ParameterizedType");
            printParameterizeType((ParameterizedType) type, level + 1);
        } else if (type instanceof WildcardType) {
            print(level, "type is an instance of WildcardType");
            printWildcardType((WildcardType) type, level + 1);
        } else {
            throw new RuntimeException();
        }
    }

    private static void printWildcardType(WildcardType type, int level) {
        Type[] lowerBounds = type.getLowerBounds();
        print(level, "WildcardType#getLowerBounds(): " + Arrays.toString(lowerBounds));
        for (Type lowerBound : lowerBounds) {
            print(level, "WildcardType#lowerBound: " + lowerBound);
            printType(lowerBound, level + 1);
        }
        Type[] upperBounds = type.getUpperBounds();
        print(level, "WildcardType#getUpperBounds(): " + Arrays.toString(upperBounds));
        for (Type upperBound : upperBounds) {
            print(level, "WildcardType#upperBound: " + upperBound);
            printType(upperBound, level + 1);
        }
    }

    private static void printParameterizeType(ParameterizedType type, int level) {
        Type ownerType = type.getOwnerType();
        print(level, "ParameterizedType#getOwnerType(): " + ownerType);
        printType(ownerType, level + 1);
        Type rawType = type.getRawType();
        print(level, "ParameterizedType#getRawType(): " + rawType);
        printType(rawType, level + 1);
        Type[] types = type.getActualTypeArguments();
        print(level, "ParameterizedType#getActualTypeArguments(): " + Arrays.toString(types));
        for (Type type1 : types) {
            print(level, "ParameterizedType#actualTypeArgument: " + type1);
            printType(type1, level + 1);
        }
    }

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

Output

 ¦- type: java.util.List<?>
 ¦- type is an instance of ParameterizedType
     ¦- ParameterizedType#getOwnerType(): null
     ¦- ParameterizedType#getRawType(): interface java.util.List
         ¦- type: interface java.util.List
         ¦- type is an instance of Class
         ¦- Class Name: java.util.List
     ¦- ParameterizedType#getActualTypeArguments(): [?]
     ¦- ParameterizedType#actualTypeArgument: ?
         ¦- type: ?
         ¦- type is an instance of WildcardType
             ¦- WildcardType#getLowerBounds(): []
             ¦- WildcardType#getUpperBounds(): [class java.lang.Object]
             ¦- WildcardType#upperBound: class java.lang.Object
                 ¦- type: class java.lang.Object
                 ¦- type is an instance of Class
                 ¦- Class Name: java.lang.Object

package com.logicbig.example.method;

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

public class GetGenericReturnTypeExample6 {
    public List<Number> process() {return null;}

    public static void main(String... args) throws NoSuchMethodException {
        Method m = GetGenericReturnTypeExample6.class.getDeclaredMethod("process");
        Type type = m.getGenericReturnType();
        printType(type, 1);
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            return;
        }
        print(level, "type: " + Objects.toString(type));
        if (type instanceof Class) {
            print(level, "type is an instance of Class");
            print(level, "Class Name: " + ((Class) type).getName());
        } else if (type instanceof ParameterizedType) {
            print(level, "type is an instance of ParameterizedType");
            printParameterizeType((ParameterizedType) type, level + 1);
        } else {
            throw new RuntimeException("Unknown type: " + type);
        }
    }

    private static void printParameterizeType(ParameterizedType type, int level) {
        Type ownerType = type.getOwnerType();
        print(level, "ParameterizedType#getOwnerType(): " + ownerType);
        printType(ownerType, level + 1);
        Type rawType = type.getRawType();
        print(level, "ParameterizedType#getRawType(): " + rawType);
        printType(rawType, level + 1);
        Type[] types = type.getActualTypeArguments();
        print(level, "ParameterizedType#getActualTypeArguments(): " + Arrays.toString(types));
        for (Type type1 : types) {
            print(level, "ParameterizedType#actualTypeArgument: " + type1);
            printType(type1, level + 1);
        }
    }

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

Output

 ¦- type: java.util.List<java.lang.Number>
 ¦- type is an instance of ParameterizedType
     ¦- ParameterizedType#getOwnerType(): null
     ¦- ParameterizedType#getRawType(): interface java.util.List
         ¦- type: interface java.util.List
         ¦- type is an instance of Class
         ¦- Class Name: java.util.List
     ¦- ParameterizedType#getActualTypeArguments(): [class java.lang.Number]
     ¦- ParameterizedType#actualTypeArgument: class java.lang.Number
         ¦- type: class java.lang.Number
         ¦- type is an instance of Class
         ¦- Class Name: java.lang.Number

Without any generics:

package com.logicbig.example.method;

import java.lang.reflect.Method;
import java.lang.reflect.Type;
import java.util.Objects;

public class GetGenericReturnTypeExample7 {
    public Number process() {return null;}

    public static void main(String... args) throws NoSuchMethodException {
        Method m = GetGenericReturnTypeExample7.class.getDeclaredMethod("process");
        Type type = m.getGenericReturnType();
        printType(type, 1);
    }

    private static void printType(Type type, int level) {
        if (type == null) {
            return;
        }
        print(level, "type: " + Objects.toString(type));
        if (type instanceof Class) {
            print(level, "type is an instance of Class");
            print(level, "Class Name: " + ((Class) type).getName());
        } else {
            throw new RuntimeException("Unknown type: " + type);
        }
    }

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

Output

 ¦- type: class java.lang.Number
 ¦- type is an instance of Class
 ¦- Class Name: java.lang.Number

Java Reflection - Method.getGenericReturnType() Examples

Class:

Method:

Examples

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See Also