Local class in ABAP
Suppose I have a global class with a public method ADD with following signature. I would like to implement with a local class inside this global class.
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The local class could be created by clicking button “Local Definitions/Implementions”:
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Now in my global class I can just delegate the ADD implementation to the local class. Notice that even ADD method is marked as public, it is still displayed as a red light in class builder, which makes sense since this ADD method in local class is not visible to outside consumers.
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Local class in ABAP in widely used in the following scenarios:
(1) ABAP unit test class
(2) The pre/post exit enhancement of class method are technically implemented via a local class in enhancement include.
For example, once you click the “Post-Exit” button below,
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You will see the source code as below, the local class LCL_ZCL_JERRY_POSTEXIT is automatically generated by class builder.
CLASS LCL_ZCL_JERRY_POSTEXIT DEFINITION DEFERRED.
CLASS CL_JERRY_TOOL DEFINITION LOCAL FRIENDS LCL_ZCL_JERRY_POSTEXIT.
CLASS LCL_ZCL_JERRY_POSTEXIT DEFINITION.
PUBLIC SECTION.
CLASS-DATA OBJ TYPE REF TO LCL_ZCL_JERRY_POSTEXIT. "#EC NEEDED
DATA CORE_OBJECT TYPE REF TO CL_JERRY_TOOL . "#EC NEEDED
INTERFACESIPO_ZCL_JERRY_POSTEXIT.
METHODS:
CONSTRUCTOR IMPORTING CORE_OBJECT
TYPE REF TO CL_JERRY_TOOL OPTIONAL.
ENDCLASS.
CLASS LCL_ZCL_JERRY_POSTEXIT IMPLEMENTATION.
METHOD CONSTRUCTOR.
ME->CORE_OBJECT = CORE_OBJECT.
ENDMETHOD.METHOD IPO_ZCL_JERRY_POSTEXIT~GET_QUERY_RESULT.
*"------------------------------------------------------------------------*
*" Declaration of POST-method, do not insert any comments here please!
*"
*"class-methods GET_QUERY_RESULT
*"importing
*"!IV_COL_WRAPPER type ref to CL_BSP_WD_COLLECTION_WRAPPER
*"changing
*"value(RV_RESULT) type ref to IF_BOL_ENTITY_COL . "#EC CI_VALPAR
*"------------------------------------------------------------------------*
**************define your own post enhancement here!!! **************ENDMETHOD.
ENDCLASS.(3) if an event handler in a given program is not intended to be reused by other programs, it could be defined as a local class within the program it is used – in this case it is not necessary to define a global class as event handler.
There are lots of such examples in ALV examples delivered by SAP, see program BCALV_GRID_DND_TREE as example.
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Inner Class in Java The above example could simply be written in Java as well. In this example the inner class lcl_local does not follow Camel naming convention since I would like to highlight that it works exactly the same as the one in ABAP example.
public class LocalClassTest{
public int add(int var1, int var2){
return new lcl_local().add(var1, var2);
}
private class lcl_local {
public int add(int var1, int var2){
return var1 + var2;
}
}
}Just exactly the same as in ABAP, the local class could not be used outside the class where it is defined.
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One typical usecase of inner class in Java is the efficient implementation of a thread-safe singleton pattern, see sample code below:
public class Example {
private static class StaticHolder {
static final MySingleton INSTANCE = new MySingleton();
}
public static MySingleton getSingleton() {
return StaticHolder.INSTANCE;
}
}“Local class” in JavaScript I use double quote in title since the function object in JavaScript are not actual “class” concept in ABAP and Java.
Below source code is a simulation of private attributes & methods in JavaScript:
function createClass(conf){
function _injectAttribute(fn){
var prototype = fn.prototype;
for(var publicName in publics){
if(!publics.hasOwnProperty(publicName))
continue;
if(typeof publics[publicName]=="function")
prototype[publicName] = function(publicName){
return function(){
return publics[publicName].apply(privates, arguments);
}
}(publicName);
else
prototype[publicName] = publics[publicName];
if(!privates[publicName])
privates[publicName] = prototype[publicName];
}
return fn;
}
var publics, privates;
publics = conf.publics;
privates = conf.privates || new Object();
var fn = function(fn){
return function(){
return fn.apply(privates, arguments);
};
}(conf.constructor || new Function());
return _injectAttribute(fn);
}var MyClass = createClass({
constructor:function(){
console.log("constructor is called: " + this.message);
},
publics:{
message:"Hello, World",
sayJavaScript:function(){
return this._message;
},
sayABAP:function(msg){
return msg + ", " + this.ABAP();
}
},
privates:{
_message: "Hello, JavaScript",
ABAP :function(){
return "ABAP";
}
}
});
var myClassInstance = new MyClass();
console.log(myClassInstance.message);
console.log(myClassInstance.sayJavaScript());
console.log(myClassInstance.sayABAP("Hello"));
console.log(myClassInstance._message);
console.log(myClassInstance.ABAP());
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Testing shows it works as expected:
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Local function in ES6 In ES6 it is possible to define a class via syntax suger class:
class Developer {
constructor(name, language) {
this.workingLanguage = language;
let _name = name;
let _getName = function() {
return _name;
};
this.getName = _getName;
}
}var Jerry = new Developer("Jerry", "Java");
var Ji = new Developer("Ji", "JavaScript");
console.log("Developer name: " + Jerry.getName());
console.log("Jerry's working language: " + Jerry.workingLanguage);
console.log("local function accessible? " + Jerry._getName);
console.log("Jerry's name: " + Jerry._name);
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Further reading I have written a series of blogs which compare the language feature among ABAP, JavaScript and Java. You can find a list of them below:
- Lazy Loading, Singleton and Bridge design pattern in JavaScript and in ABAP
- Functional programming – Simulate Curry in ABAP
- Functional Programming – Try Reduce in JavaScript and in ABAP
- Simulate Mockito in ABAP
- A simulation of Java Spring dependency injection annotation @Inject in ABAP
- Singleton bypass – ABAP and Java
- Weak reference in ABAP and Java
- Fibonacci Sequence in ES5, ES6 and ABAP
- Java byte code and ABAP Load
- How to write a correct program rejected by compiler: Exception handling in Java and in ABAP
- An small example to learn Garbage collection in Java and in ABAP
- String Template in ABAP, ES6, Angular and React
- Try to access static private attribute via ABAP RTTI and Java Reflection
- Local class in ABAP, Java and JavaScript
- Integer in ABAP, Java and JavaScript
- Covariance in Java and simulation in ABAP
- Various Proxy Design Pattern implementation variants in Java and ABAP
- Tag(Marker) Interface in ABAP and Java
- Bitwise operation ( OR, AND, XOR ) on ABAP Integer
- ABAP ICF handler and Java Servlet
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