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

@Test
public static void testWhileLoopNoIteration() throws Throwable {
    // a while loop that never executes its body because the predicate evaluates to false immediately
    MethodHandle loop = MethodHandles.whileLoop(While.MH_initString, While.MH_predString, While.MH_stepString);
    assertEquals(While.MT_string, loop.type());
    assertEquals("a", loop.invoke());
}
 

@Test
public static void testWhileBadInit() throws Throwable {
    boolean caught = false;
    try {
        While w = new While();
        MethodHandle loop = MethodHandles.whileLoop(MethodHandles.empty(methodType(void.class, char.class)),
                                                    While.MH_voidPred.bindTo(w),
                                                    While.MH_voidBody.bindTo(w));
    } catch (IllegalArgumentException iae) {
        assertEquals("loop initializer must match: (char)void != (int)void", iae.getMessage());
        caught = true;
    }
    assertTrue(caught);
}
 

@Test
public static void testWhileVoidInit() throws Throwable {
    While w = new While();
    int v = 5;
    MethodHandle loop = MethodHandles.whileLoop(While.MH_voidInit.bindTo(w), While.MH_voidPred.bindTo(w),
            While.MH_voidBody.bindTo(w));
    assertEquals(While.MT_void, loop.type());
    loop.invoke(v);
    assertEquals(v, w.i);
}
 

@Test(dataProvider = "nullArgs", expectedExceptions = NullPointerException.class)
public static void testWhileNullArgs(MethodHandle pred, MethodHandle body) {
    MethodHandles.whileLoop(null, pred, body);
}
 

@Test(dataProvider = "nullArgs", expectedExceptions = NullPointerException.class)
public static void testDoWhileNullArgs(MethodHandle body, MethodHandle pred) {
    MethodHandles.whileLoop(null, body, pred);
}