How To Create Generic Method In Java

Java Generic Methods Examples

In this article, we will learn how to write a generic method with examples.

The Syntax for Defining Generic Method

              <type-              Parameters              >              return_type method_name(parameter list) {                              //                ..              }

The syntax for a generic method includes a list of type parameters, inside angle brackets, which appears before the method's return type. For static generic methods, the type parameter section must appear before the method's return type.

Java Generic Methods Examples

Generic Methods Example to Convert Array to ArrayList

In this example. we have used Java 8 features so JDK 8 or later is required to compile and execute this program.

              import              java.util.Arrays;              import              java.util.List;              import              java.util.function.Function;              import              java.util.stream.Collectors;              /**                              * Generic methods example to convert array to list.                              *                @author                javaguides.net                              *                              */                            public              class              GenericMethodsExamples              {                              //                definition of a generic method              public              static              <T>              List<T>              fromArrayToList(T[]              a) {              return              Arrays              .stream(a).collect(Collectors              .toList());     }                              //                definition of a generic method              public              static              <T,                G>              List<G>              fromArrayToList(T[]              a,              Function<T,                G>              mapperFunction) {              return              Arrays              .stream(a).map(mapperFunction).collect(Collectors              .toList());     }                              //                example of a generic method that has Number as an upper bound for T              public              static              <T                extends                Number>              List<T>              fromArrayToListWithUpperBound(T[]              a) {              return              Arrays              .stream(a).collect(Collectors              .toList());     }              public              static              void              main(String[]              args) {                              //                testing the generic method with Integer              Integer[] intArray              =              {              1,              2,              3,              4,              5              };              List<Integer>              list              =              fromArrayToList(intArray);          list.forEach(element              -              >              System              .out.println(element));                              //                testing the generic method with String              String[] stringArray              =              {                              "hello1"              ,                              "hello2"              ,                              "hello3"              ,                              "hello4"              ,                              "hello5"                            };              List<String>              strList              =              fromArrayToList(stringArray);          strList.forEach(element              -              >              System              .out.println(element));                              //                testing the generic method with Integer and String type              Integer[] intArr              =              {              1,              2,              3,              4,              5              };              List<String>              stringList              =              fromArrayToList(intArr,              Object              ::toString);          stringList.forEach(element              -              >              System              .out.println(element));      } }

Output:

            1 2 3 4 5 hello1 hello2 hello3 hello4 hello5 1 2 3 4 5

Create Generic equals and compare Method Example

Let's create Generic class GenType.

              public              class              GenType<T> {              private              T              t;              public              T              get() {              return              this              .t;     }              public              void              set(T              t1) {              this              .t              =              t1;     } }

Let's write generic equals and compare methods to check equality.

              public              static              <              T              >              boolean              isEqual(GenType<T>              g1,              GenType<T>              g2){              return              g1.get().equals(g2.get()); }              public              static              <              T              extends              Comparable<T>              >              int              compare(T              t1,              T              t2){              return              t1.compareTo(t2); }

The complete example of the above generic methods and it's testing code.

              public              class              GenericsMethods              {                              //Generics in method              public              static              <T>              boolean              isEqual(GenType<T>              g1,              GenType<T>              g2){              return              g1.get().equals(g2.get());     }              public              static              <T                extends                Comparable<T>>              int              compare(T              t1,              T              t2){              return              t1.compareTo(t2);     }              public              static              void              main(String              args[]){              GenType<String>              g1              =              new              GenType<>();          g1.set(                "demo"              );              GenType<String>              g2              =              new              GenType<>();          g2.set(                "demo"              );              boolean              isEqual              =              GenericsMethods              .              <              String              >isEqual(g1, g2);              System              .out.println(isEqual);                              //above statement can be written simply as              isEqual              =              GenericsMethods              .isEqual(g1, g2);              System              .out.println(isEqual);              System              .out.println(GenericsMethods              .compare(                "abc"              ,                "abc"              ));     } }

Output:

            true true 0

Related Java Generics Examples

Core Java Java Generics