method overloading - Hierarchy issue on Composite with Java -
i'm trying use composite pattern on java in order report, , i'm forgetting how hierarchy , method overload work.
let's have following models:
public class product { public string get(){ return "product"; } } public class bproduct extends product { public string getb() { return "bbbbb"; } } public class cproduct extends product { public string getc() { return "ccccc"; } } and following converters:
import java.util.list; public class converter { private list<converter> converters; public converter() { } public converter(list<converter> converters) { this.converters = converters; } public void execute(product product) { (converter converter : converters) { converter.execute(product); } } } public class bconverter extends converter { @override public void execute(product product) { innerexecute(product); } public void innerexecute(product product) { system.out.println(product.get() + " done on b normal."); } public void innerexecute(bproduct b) { system.out.println(b.getb() + " done on b special."); } } public class cconverter extends converter { @override public void execute(product product) { system.out.println(product.get() + " done on c normal."); } public void execute(cproduct c) { system.out.println(c.getc() + " done on c special."); } } testing following test:
import java.util.arraylist; import java.util.list; import org.junit.test; public class productconvertertest { @test public void test() { list<converter> converters = new arraylist<>(); converters.add(new bconverter()); converters.add(new cconverter()); converter converter = new converter(converters); list<product> list = new arraylist<>(); list.add(new product()); list.add(new bproduct()); list.add(new cproduct()); (product product : list) { converter.execute(product); } } } gets output:
product done on b normal. product done on c normal. product done on b normal. product done on c normal. product done on b normal. product done on c normal. when want is:
product done on b normal. product done on c normal. bbbbb done on b special. product done on c normal. product done on b normal. ccccc done on c special. note: want without using instanceof. know how it. want know if can done without it.
the reason behaviour #execute method overloaded. choice of overloaded method invoke made @ compile time. in order make work want have use dynamic selection, lead either instanceof check or overwriting methods or pass/retrieve class of product , compare like:
public class converter { private list<converter> converters; public converter() { } public converter(list<converter> converters) { this.converters = converters; } public void execute(product product) { (converter converter : converters) { converter.execute(product); } } } public class bconverter extends converter { @override public void execute(product product) { if (product.getclass() == bproduct.class) { innerexecute((bproduct)product); } else { innerexecute(product); } } public void innerexecute(product product) { system.out.println(product.get() + " done on b normal."); } public void innerexecute(bproduct b) { system.out.println(b.getb() + " done on b special."); } } public class cconverter extends converter { @override public void execute(product product) { if (product.getclass() == cproduct.class) { innerexecute((cproduct)product); } else { innerexecute(product); } } public void innerexecute(product product) { system.out.println(product.get() + " done on c normal."); } public void innerexecute(cproduct b) { system.out.println(b.getc() + " done on c special."); } }
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