So lets see how we can test for ”param is valid type”.<\/p>\n
Bar<\/b>
\n[code lang=”java”]
\npublic class Bar {
\n}
\n[\/code]<\/p>\n
Test<\/b> public static void test1(Object a) { These translate into this<\/p>\n Bar Disassembled: javap -c Bar<\/b> } Test Disassembled: javap -c Test<\/b> public static void test1(java.lang.Object); public static void test2(java.lang.Object); public static void test3(java.lang.Object); static {}; } So what we learn from this, hopefully something. At least it seems that it’s not good idea trying to outsmart compiler, and secondly it doesn’t matter. I.e. I believe that in this case there isn’t any differerence in performance, however, it seems that instanceof version creates slightly shorter bytecode. However, must<\/b> be noted that there is various very valid reasons for exact class equality instead of For example,<\/p>\n Ensuring that [code lang=”java”] [code lang=”java”] Strict class equality ensures here that equals() contract is implemented properly, with If you’ve developed with java long enough, you surely have had enough of horror stories of equals() -methods, which implement interesting hacks to provide equality between Apples and Oranges (naturally without any documentation, and at some point of time those hacks start to haunt you when some refactoring is done, and fixing hacks is difficult, since there ain’t any clear traces why such strange things exists at all).<\/p>\n PS.<\/b> Please notice that ”a != null” checks are irrelevant in the Test class, since it conforms into standard safe API spec convention. This convention states that all values (param or return) are NON-NULL<\/b> unless otherwise stated. I.e. makes programming much easier, since that is the best default value. Thus when you conform to this convention, safe API spec is specified with minimal effort, and it also promotes using safe methods (i.e. no horror stories of methods, without any kind of specifications, returning randomly null values, which can cumulate incredible amount of highly unclear and unmaintainable code in the full call chain for such methods).<\/p>\n
\n[code lang=”java”]
\npublic class Test {
\n private static final Class
\n if (a instanceof Bar) {
\n int x = 0;
\n }
\n }
\n public static void test2(Object a) {
\n if (a.getClass() == Bar.class) {
\n int x = 0;
\n }
\n }
\n public static void test3(Object a) {
\n if (a.getClass() == CLS) {
\n int x = 0;
\n }
\n }
\n}
\n[\/code]<\/p>\n
\n[code lang=”java”]
\npublic class Bar extends java.lang.Object{
\npublic Bar();
\n Code:
\n 0: aload_0
\n 1: invokespecial #1; \/\/Method java\/lang\/Object.”
\n 4: return<\/p>\n
\n[\/code]<\/p>\n
\n[code lang=”java”]
\npublic class Test extends java.lang.Object{
\npublic Test();
\n Code:
\n 0: aload_0
\n 1: invokespecial #1; \/\/Method java\/lang\/Object.”
\n 4: return<\/p>\n
\n Code:
\n 0: aload_0
\n 1: instanceof #2; \/\/class Bar
\n 4: ifeq 9
\n 7: iconst_0
\n 8: istore_1
\n 9: return<\/p>\n
\n Code:
\n 0: aload_0
\n 1: invokevirtual #3; \/\/Method java\/lang\/Object.getClass:()Ljava\/lang\/Class;
\n 4: ldc_w #2; \/\/class Bar
\n 7: if_acmpne 12
\n 10: iconst_0
\n 11: istore_1
\n 12: return<\/p>\n
\n Code:
\n 0: aload_0
\n 1: invokevirtual #3; \/\/Method java\/lang\/Object.getClass:()Ljava\/lang\/Class;
\n 4: getstatic #4; \/\/Field CLS:Ljava\/lang\/Class;
\n 7: if_acmpne 12
\n 10: iconst_0
\n 11: istore_1
\n 12: return<\/p>\n
\n Code:
\n 0: ldc_w #2; \/\/class Bar
\n 3: putstatic #4; \/\/Field CLS:Ljava\/lang\/Class;
\n 6: return<\/p>\n
\n[\/code]<\/p>\ninstanceof<\/code>.<\/p>\nequals()<\/code> produces correct results<\/p>\n
\npublic class Foo {
\n public boolean equals(Object o) {
\n if (o == this) {
\n return true;
\n } else if (o == null) {
\n return false;
\n }
\n if (o.getClass() == getClass() {
\n \/\/ …
\n }
\n return false;
\n }
\n}
\n[\/code]<\/p>\n
\npublic class Bar extends Foo {
\n \/\/ …
\n}
\n[\/code]<\/p>\ninstanceof<\/code>, Foo could equal to Bar, but Bar would not equal to Foo.<\/p>\n