Comparing Java References
jequals.Rd.jequals function can be used to determine whether two objects
are equal. In addition, it allows mixed comparison of non-Java object
for convenience, unless strict comparison is desired.
The binary operators == and != are mapped to
(non-strict) call to .jequals for convenience.
.jcompare compares two objects in the sense of the
java.lang.Comparable interface.
The binary operators <, >, <=, >= are mapped
to calls to .jcompare for convenience
Value
.jequals returns TRUE if both object
are considered equal, FALSE otherwise.
.jcompare returns the result of the compareTo java method
of the object a applied to b
Methods
- !=
signature(e1 = "ANY", e2 = "jobjRef"): ...- !=
signature(e1 = "jobjRef", e2 = "jobjRef"): ...- !=
signature(e1 = "jobjRef", e2 = "ANY"): ...- ==
signature(e1 = "ANY", e2 = "jobjRef"): ...- ==
signature(e1 = "jobjRef", e2 = "jobjRef"): ...- ==
signature(e1 = "jobjRef", e2 = "ANY"): ...- <
signature(e1 = "ANY", e2 = "jobjRef"): ...- <
signature(e1 = "jobjRef", e2 = "jobjRef"): ...- <
signature(e1 = "jobjRef", e2 = "ANY"): ...- >
signature(e1 = "ANY", e2 = "jobjRef"): ...- >
signature(e1 = "jobjRef", e2 = "jobjRef"): ...- >
signature(e1 = "jobjRef", e2 = "ANY"): ...- >=
signature(e1 = "ANY", e2 = "jobjRef"): ...- >=
signature(e1 = "jobjRef", e2 = "jobjRef"): ...- >=
signature(e1 = "jobjRef", e2 = "ANY"): ...- <=
signature(e1 = "ANY", e2 = "jobjRef"): ...- <=
signature(e1 = "jobjRef", e2 = "jobjRef"): ...- <=
signature(e1 = "jobjRef", e2 = "ANY"): ...
Details
.jequals compares two Java objects by calling equals
method of one of the objects and passing the other object as its
argument. This allows Java objects to define the `equality' in
object-dependent way.
In addition, .jequals allows the comparison of Java object to
other scalar R objects. This is done by creating a temporary Java
object that corresponds to the R object and using it for a call to the
equals method. If such conversion is not possible a warning is
produced and the result it FALSE. The automatic conversion
will be avoided if strict parameter is set to TRUE.
NULL values in a or b are replaced by Java
null-references and thus .jequals(NULL,NULL) is TRUE.
If neither a and b are Java objects (with the exception
of both being NULL) then the result is identical to that of
all.equal(a,b).
Neither comparison operators nor .jequals supports vectors and
returns FALSE in that case. A warning is also issued unless
strict comparison was requested.
Note
Don't use x == NULL to check for
null-references, because x could be NULL and thus
the result would be an empty vector. Use is.jnull
instead.
(In theory is.jnull and x == .jnull() are the the same,
but is.jnull is more efficient.)
Examples
s <- .jnew("java/lang/String", "foo")
.jequals(s, "foo") # TRUE
#> [1] TRUE
.jequals(s, "foo", strict=TRUE) # FALSE - "foo" is not a Java object
#> [1] FALSE
t <- s
.jequals(s, t, strict=TRUE) # TRUE
#> [1] TRUE
s=="foo" # TRUE
#> [1] TRUE
Double <- J("java.lang.Double")
d1 <- new( Double, 0.0 )
#> Error in .jcall("RJavaTools", "Ljava/lang/Object;", "newInstance", class, .jarray(p, "java/lang/Object", dispatch = FALSE), .jarray(pc, "java/lang/Class", dispatch = FALSE), evalString = FALSE, evalArray = FALSE, use.true.class = TRUE): RcallMethod: cannot determine object class
d2 <- new( Double, 1.0 )
#> Error in .jcall("RJavaTools", "Ljava/lang/Object;", "newInstance", class, .jarray(p, "java/lang/Object", dispatch = FALSE), .jarray(pc, "java/lang/Class", dispatch = FALSE), evalString = FALSE, evalArray = FALSE, use.true.class = TRUE): RcallMethod: cannot determine object class
d3 <- new( Double, 0.0 )
#> Error in .jcall("RJavaTools", "Ljava/lang/Object;", "newInstance", class, .jarray(p, "java/lang/Object", dispatch = FALSE), .jarray(pc, "java/lang/Class", dispatch = FALSE), evalString = FALSE, evalArray = FALSE, use.true.class = TRUE): RcallMethod: cannot determine object class
d1 < d2
#> Error: object 'd1' not found
d1 <= d3
#> Error: object 'd1' not found
d1 >= d3
#> Error: object 'd1' not found
d1 > d2
#> Error: object 'd1' not found
# cannot compare a Double and a String
try( d1 < "foo" )
#> Error in eval(expr, envir) : object 'd1' not found
# but can compare a Double and an Integer
d1 < 10L
#> Error: object 'd1' not found
#> Error: object 'd1' not found