How often do you think about possible changes in your API? Do you consider that something required could become optional in future? How about compatibility of such change? One of this changes is going from primitive (e. g. Let’s start with simple DTO class public int getF1(){ public void setF1(int f1){ \/\/ other fields and methods omitted Let’s use it in compile it:<\/p>\n and run:<\/p>\n It works.<\/p>\n Now suppose our business requirements have changed. So we provide next iteration of public Integer getF1(){ public void setF1(Integer f1){ \/\/ other fields and methods omitted We compile only the new and run it with old Wow! It does not work…<\/p>\n We can use public static void main(java.lang.String…); The most important are 11th and 18th instructions of Next let’s compile the and use public static void main(java.lang.String…); Now we see the difference. The These differences do not allow us to use the We have We will compile It runs great as expected with but with Groovy is immune to such change.<\/p>\nint<\/code>) to its wrapped type (e. g. Integer<\/code>). Let’s check it out.<\/p>\nAPI – first iteration<\/span><\/h2>\n
Dep<\/code> in our public API.<\/p>\npublic class Dep {\r\n private int f1;<\/pre>\n
\nreturn f1;
\n}<\/p>\n
\nthis.f1 = f1;
\n}<\/p>\n
\n}<\/p>\nf1<\/code> is obligatory field that never will be null.<\/p>\nMain<\/code> class:<\/p>\npublic class Main {\r\n public static void main(String... args) {\r\n Dep dep = new Dep();\r\n dep.setF1(123);\r\n System.out.println(dep.getF1());\r\n }\r\n}<\/pre>\n$ javac depInt\/Dep.java\r\n$ javac -cp depInt main\/Main.java<\/pre>\n
$ java -cp depInt:main Main\r\n123<\/pre>\n
API – obligatory field become optional<\/span><\/h2>\n
f1<\/code> is not longer obligatory and we want possibility to set it to null<\/code>.<\/p>\nDep<\/code> class where f1<\/code> field has type Integer<\/code>.<\/p>\npublic class Dep {\r\n private Integer f1;<\/pre>\n
\nreturn f1;
\n}<\/p>\n
\nthis.f1 = f1;
\n}<\/p>\n
\n}<\/p>\nDep<\/code> class because we do not want to change the Main<\/code> class:<\/p>\n$ javac depInteger\/Dep.java<\/pre>\n
Main<\/code>:<\/p>\n$ java -cp depInteger:main Main\r\nException in thread \"main\" java.lang.NoSuchMethodError: Dep.setF1(I)V\r\n at Main.main(Main.java:4)<\/pre>\n
Why does it not work?<\/h2>\n
javap<\/code> tool to investigate Main<\/code> class.<\/p>\n$ javap -c main\/Main.class\r\nCompiled from \"Main.java\"\r\npublic class Main {\r\n public Main();\r\n Code:\r\n 0: aload_0\r\n 1: invokespecial #1 \/\/ Method java\/lang\/Object.\"<init>\":()V\r\n 4: return<\/pre>\n
\nCode:
\n0: new #2 \/\/ class Dep
\n3: dup
\n4: invokespecial #3 \/\/ Method Dep.”<init>”:()V
\n7: astore_1
\n8: aload_1
\n9: bipush 123
\n11: invokevirtual #4 \/\/ Method Dep.setF1:(I)V
\n14: getstatic #5 \/\/ Field java\/lang\/System.out:Ljava\/io\/PrintStream;
\n17: aload_1
\n18: invokevirtual #6 \/\/ Method Dep.getF1:()I
\n21: invokevirtual #7 \/\/ Method java\/io\/PrintStream.println:(I)V
\n24: return
\n}<\/p>\nmain<\/code> method. Main<\/code> lookups for methods which use int<\/code> (I<\/code> in method signature).<\/p>\nMain<\/code> class with Dep<\/code> which has f1<\/code> of type Integer<\/code>:<\/p>\njavac -cp depInteger main\/Main.java<\/pre>\n
javap<\/code> on this class:<\/p>\n$ javap -c main\/Main.class\r\nCompiled from \"Main.java\"\r\npublic class Main {\r\n public Main();\r\n Code:\r\n 0: aload_0\r\n 1: invokespecial #1 \/\/ Method java\/lang\/Object.\"<init>\":()V\r\n 4: return<\/pre>\n
\nCode:
\n0: new #2 \/\/ class Dep
\n3: dup
\n4: invokespecial #3 \/\/ Method Dep.”<init>”:()V
\n7: astore_1
\n8: aload_1
\n9: bipush 123
\n11: invokestatic #4 \/\/ Method java\/lang\/Integer.valueOf:(I)Ljava\/lang\/Integer;
\n14: invokevirtual #5 \/\/ Method Dep.setF1:(Ljava\/lang\/Integer;)V
\n17: getstatic #6 \/\/ Field java\/lang\/System.out:Ljava\/io\/PrintStream;
\n20: aload_1
\n21: invokevirtual #7 \/\/ Method Dep.getF1:()Ljava\/lang\/Integer;
\n24: invokevirtual #8 \/\/ Method java\/io\/PrintStream.println:(Ljava\/lang\/Object;)V
\n27: return
\n}<\/p>\nmain<\/code> method:<\/p>\n\n
int<\/code> to Integer<\/code> in instruction 11th,<\/li>\nsetF1<\/code> which takes parameter of type Integer<\/code> (Ljava\/lang\/Integer;<\/code>) in instruction 14th,<\/li>\ngetF1<\/code> which returns Integer<\/code> in instruction 21st.<\/li>\n<\/ul>\nMain<\/code> class with Dep<\/code> without recompilation if we change f1<\/code>.<\/p>\nHow about Groovy?<\/h2>\n
GroovyMain<\/code> class which do the same as Main<\/code> class written in Java.<\/p>\nclass GroovyMain {\r\n static void main(String... args) {\r\n Dep dep = new Dep(f1: 123)\r\n println(dep.f1)\r\n }\r\n}<\/pre>\nGroovyMain<\/code> class only with Dep<\/code> which uses int<\/code>:<\/p>\n$ groovyc -cp lib\/groovy-all-2.4.5.jar:depInt -d main main\/GroovyMain.groovy<\/pre>\n
int<\/code>:<\/p>\n$ java -cp lib\/groovy-all-2.4.5.jar:depInt:main GroovyMain\r\n123<\/pre>\n
Integer<\/code>… It works the same!<\/p>\n$ java -cp lib\/groovy-all-2.4.5.jar:depInteger:main GroovyMain\r\n123<\/pre>\n
With CompileStatic<\/h3>\n