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BAEL-1441: Method Handles in Java 9 (#3565) 

* Added MethodHandles API code

* Added Reflection API example for comparison
This commit is contained in:
Carlo Corti 2018-02-27 14:33:28 +01:00 committed by Grzegorz Piwowarek
parent ea306bec5f
commit 9801a08599
2 changed files with 169 additions and 0 deletions
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17
core-java-9/src/main/java/com/baeldung/java9/methodhandles/Book.java Normal file
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package com.baeldung.java9.methodhandles;
public class Book {
String id;
String title;
public Book(String id, String title) {
this.id = id;
this.title = title;
}
@SuppressWarnings("unused")
private String formatBook() {
return id + " > " + title;
}
}

152
core-java-9/src/test/java/com/baeldung/java9/methodhandles/MethodHandlesTest.java Normal file
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package com.baeldung.java9.methodhandles;
import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.*;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.invoke.WrongMethodTypeException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.List;
import org.junit.Test;
/**
* Test case for the {@link MethodHandles} API
*/
public class MethodHandlesTest {
@Test
public void givenConcatMethodHandle_whenInvoked_thenCorrectlyConcatenated() throws Throwable {
MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
MethodType mt = MethodType.methodType(String.class, String.class);
MethodHandle concatMH = publicLookup.findVirtual(String.class, "concat", mt);
String output = (String) concatMH.invoke("Effective ", "Java");
assertEquals("Effective Java", output);
}
@Test
public void givenAsListMethodHandle_whenInvokingWithArguments_thenCorrectlyInvoked() throws Throwable {
MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
MethodType mt = MethodType.methodType(List.class, Object[].class);
MethodHandle asListMH = publicLookup.findStatic(Arrays.class, "asList", mt);
List<Integer> list = (List<Integer>) asListMH.invokeWithArguments(1, 2);
assertThat(Arrays.asList(1, 2), is(list));
}
@Test
public void givenConstructorMethodHandle_whenInvoked_thenObjectCreatedCorrectly() throws Throwable {
MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
MethodType mt = MethodType.methodType(void.class, String.class);
MethodHandle newIntegerMH = publicLookup.findConstructor(Integer.class, mt);
Integer integer = (Integer) newIntegerMH.invoke("1");
assertEquals(1, integer.intValue());
}
@Test
public void givenAFieldWithoutGetter_whenCreatingAGetter_thenCorrectlyInvoked() throws Throwable {
MethodHandles.Lookup lookup = MethodHandles.lookup();
MethodHandle getTitleMH = lookup.findGetter(Book.class, "title", String.class);
Book book = new Book("ISBN-1234", "Effective Java");
assertEquals("Effective Java", getTitleMH.invoke(book));
}
@Test
public void givenPrivateMethod_whenCreatingItsMethodHandle_thenCorrectlyInvoked() throws Throwable {
MethodHandles.Lookup lookup = MethodHandles.lookup();
Method formatBookMethod = Book.class.getDeclaredMethod("formatBook");
formatBookMethod.setAccessible(true);
MethodHandle formatBookMH = lookup.unreflect(formatBookMethod);
Book book = new Book("ISBN-123", "Java in Action");
assertEquals("ISBN-123 > Java in Action", formatBookMH.invoke(book));
}
@Test
public void givenReplaceMethod_whenUsingReflectionAndInvoked_thenCorrectlyReplaced() throws Throwable {
Method replaceMethod = String.class.getMethod("replace", char.class, char.class);
String string = (String) replaceMethod.invoke("jovo", 'o', 'a');
assertEquals("java", string);
}
@Test
public void givenReplaceMethodHandle_whenInvoked_thenCorrectlyReplaced() throws Throwable {
MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
MethodType mt = MethodType.methodType(String.class, char.class, char.class);
MethodHandle replaceMH = publicLookup.findVirtual(String.class, "replace", mt);
String replacedString = (String) replaceMH.invoke("jovo", Character.valueOf('o'), 'a');
assertEquals("java", replacedString);
}
@Test
public void givenReplaceMethodHandle_whenInvokingExact_thenCorrectlyReplaced() throws Throwable {
MethodHandles.Lookup lookup = MethodHandles.lookup();
MethodType mt = MethodType.methodType(String.class, char.class, char.class);
MethodHandle replaceMH = lookup.findVirtual(String.class, "replace", mt);
String s = (String) replaceMH.invokeExact("jovo", 'o', 'a');
assertEquals("java", s);
}
@Test
public void givenSumMethodHandle_whenInvokingExact_thenSumIsCorrect() throws Throwable {
MethodHandles.Lookup lookup = MethodHandles.lookup();
MethodType mt = MethodType.methodType(int.class, int.class, int.class);
MethodHandle sumMH = lookup.findStatic(Integer.class, "sum", mt);
int sum = (int) sumMH.invokeExact(1, 11);
assertEquals(12, sum);
}
@Test(expected = WrongMethodTypeException.class)
public void givenSumMethodHandleAndIncompatibleArguments_whenInvokingExact_thenException() throws Throwable {
MethodHandles.Lookup lookup = MethodHandles.lookup();
MethodType mt = MethodType.methodType(int.class, int.class, int.class);
MethodHandle sumMH = lookup.findStatic(Integer.class, "sum", mt);
sumMH.invokeExact(Integer.valueOf(1), 11);
}
@Test
public void givenSpreadedEqualsMethodHandle_whenInvokedOnArray_thenCorrectlyEvaluated() throws Throwable {
MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
MethodType mt = MethodType.methodType(boolean.class, Object.class);
MethodHandle equalsMH = publicLookup.findVirtual(String.class, "equals", mt);
MethodHandle methodHandle = equalsMH.asSpreader(Object[].class, 2);
assertTrue((boolean) methodHandle.invoke(new Object[] { "java", "java" }));
assertFalse((boolean) methodHandle.invoke(new Object[] { "java", "jova" }));
}
@Test
public void givenConcatMethodHandle_whenBindToAString_thenCorrectlyConcatenated() throws Throwable {
MethodHandles.Lookup publicLookup = MethodHandles.publicLookup();
MethodType mt = MethodType.methodType(String.class, String.class);
MethodHandle concatMH = publicLookup.findVirtual(String.class, "concat", mt);
MethodHandle bindedConcatMH = concatMH.bindTo("Hello ");
assertEquals("Hello World!", bindedConcatMH.invoke("World!"));
}
}