java.lang.invoke.MethodHandles#loop ( )源码实例Demo

@Test
public static void testLoopFac() throws Throwable {
    MethodHandle[] counterClause = new MethodHandle[]{Fac.MH_zero, Fac.MH_inc};
    MethodHandle[] accumulatorClause = new MethodHandle[]{Fac.MH_one, Fac.MH_mult, Fac.MH_pred, Fac.MH_fin};
    MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
    assertEquals(Fac.MT_fac, loop.type());
    assertEquals(120, loop.invoke(5));
}
 

@Test
public static void testLoopFacNullInit() throws Throwable {
    // null initializer for counter, should initialize to 0
    MethodHandle[] counterClause = new MethodHandle[]{null, Fac.MH_inc};
    MethodHandle[] accumulatorClause = new MethodHandle[]{Fac.MH_one, Fac.MH_mult, Fac.MH_pred, Fac.MH_fin};
    MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
    assertEquals(Fac.MT_fac, loop.type());
    assertEquals(120, loop.invoke(5));
}
 

@Test
public static void testLoopNullInit() throws Throwable {
    // null initializer for counter, should initialize to 0, one-clause loop
    MethodHandle[] counterClause = new MethodHandle[]{null, Loop.MH_inc, Loop.MH_pred, Loop.MH_fin};
    MethodHandle loop = MethodHandles.loop(counterClause);
    assertEquals(Loop.MT_loop, loop.type());
    assertEquals(10, loop.invoke(10));
}
 

@Test
public static void testLoopVoid1() throws Throwable {
    // construct a post-checked loop that only does one iteration and has a void body and void local state
    MethodHandle loop = MethodHandles.loop(new MethodHandle[]{Empty.MH_f, Empty.MH_f, Empty.MH_pred, null});
    assertEquals(MethodType.methodType(void.class), loop.type());
    loop.invoke();
}
 

@Test
public static void testLoopVoid2() throws Throwable {
    // construct a post-checked loop that only does one iteration and has a void body and void local state,
    // initialized implicitly from the step type
    MethodHandle loop = MethodHandles.loop(new MethodHandle[]{null, Empty.MH_f, Empty.MH_pred, null});
    assertEquals(MethodType.methodType(void.class), loop.type());
    loop.invoke();
}
 

@Test
public static void testLoopVoid3() throws Throwable {
    // construct a post-checked loop that only does one iteration and has a void body and void local state,
    // and that has a void finalizer
    MethodHandle loop = MethodHandles.loop(new MethodHandle[]{null, Empty.MH_f, Empty.MH_pred, Empty.MH_f});
    assertEquals(MethodType.methodType(void.class), loop.type());
    loop.invoke();
}
 

@Test
public static void testLoopFacWithVoidState() throws Throwable {
    // like testLoopFac, but with additional void state that outputs a dot
    MethodHandle[] counterClause = new MethodHandle[]{Fac.MH_zero, Fac.MH_inc};
    MethodHandle[] accumulatorClause = new MethodHandle[]{Fac.MH_one, Fac.MH_mult, Fac.MH_pred, Fac.MH_fin};
    MethodHandle[] dotClause = new MethodHandle[]{null, Fac.MH_dot};
    MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause, dotClause);
    assertEquals(Fac.MT_fac, loop.type());
    assertEquals(120, loop.invoke(5));
}
 

@Test
public static void testLoopVoidInt() throws Throwable {
    // construct a post-checked loop that only does one iteration and has a void body and void local state,
    // and that returns a constant
    MethodHandle loop = MethodHandles.loop(new MethodHandle[]{null, Empty.MH_f, Empty.MH_pred, Empty.MH_c});
    assertEquals(MethodType.methodType(int.class), loop.type());
    assertEquals(23, loop.invoke());
}
 

@Test
public static void testLoopWithVirtuals() throws Throwable {
    // construct a loop (to calculate factorial) that uses a mix of static and virtual methods
    MethodHandle[] counterClause = new MethodHandle[]{null, LoopWithVirtuals.permute(LoopWithVirtuals.MH_inc)};
    MethodHandle[] accumulatorClause = new MethodHandle[]{
            // init function must indicate the loop arguments (there is no other means to determine them)
            MethodHandles.dropArguments(LoopWithVirtuals.MH_one, 0, LoopWithVirtuals.class),
            LoopWithVirtuals.permute(LoopWithVirtuals.MH_mult),
            LoopWithVirtuals.permute(LoopWithVirtuals.MH_pred),
            LoopWithVirtuals.permute(LoopWithVirtuals.MH_fin)
    };
    MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
    assertEquals(LoopWithVirtuals.MT_loop, loop.type());
    assertEquals(120, loop.invoke(new LoopWithVirtuals(), 5));
}
 

@Test
public static void testLoopOmitPred() throws Throwable {
    // construct a loop to calculate factorial that omits a predicate
    MethodHandle[] counterClause = new MethodHandle[]{null, Fac.MH_inc, null, Fac.MH_fin};
    MethodHandle[] accumulatorClause = new MethodHandle[]{Fac.MH_one, Fac.MH_mult, Fac.MH_pred, Fac.MH_fin};
    MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
    assertEquals(Fac.MT_fac, loop.type());
    assertEquals(120, loop.invoke(5));
}
 

static void testLongSignature(int loopArgs, boolean excessive, boolean run) {
    int nClauses = ARG_LIMIT - loopArgs + (excessive ? 1 : 0);

    System.out.print((excessive ? "(EXCESSIVE)" : "(LONG     )") + " arguments: " + loopArgs + ", clauses: " + nClauses + " -> ");

    // extend init to denote what arguments the loop should accept
    Class<?>[] argTypes = new Class<?>[loopArgs];
    Arrays.fill(argTypes, int.class);
    MethodHandle init = MethodHandles.dropArguments(INIT, 0, argTypes);

    // build clauses
    MethodHandle[][] clauses = new MethodHandle[nClauses][];
    MethodHandle[] clause = {init, STEP, PRED_T, FINI};
    MethodHandle[] fclause = {init, STEP, PRED_F, FINI};
    Arrays.fill(clauses, clause);
    clauses[nClauses - 1] = fclause; // make the last clause terminate the loop

    try {
        MethodHandle loop = MethodHandles.loop(clauses);
        if (excessive) {
            throw new AssertionError("loop construction should have failed");
        } else if (run) {
            int r;
            if (loopArgs == 0) {
                r = (int) loop.invoke();
            } else {
                Object[] args = new Object[loopArgs];
                Arrays.fill(args, 0);
                r = (int) loop.invokeWithArguments(args);
            }
            System.out.println("SUCCEEDED (OK) -> " + r);
        } else {
            System.out.println("SUCCEEDED (OK)");
        }
    } catch (IllegalArgumentException iae) {
        if (excessive) {
            System.out.println("FAILED    (OK)");
        } else {
            iae.printStackTrace(System.out);
            throw new AssertionError("loop construction should not have failed (see above)");
        }
    } catch (Throwable t) {
        t.printStackTrace(System.out);
        throw new AssertionError("unexpected failure (see above)");
    }
}