ArrayList confusion

[Phil Dixon]

Could someone shed some light on the ArrayList below.

public class ClassA {
public ClassA() {
System.out.println("This is ClassA");
}
}

import java.util.ArrayList;
public class ClassB {
public static void main (String[] args) {
ArrayList<ClassA> myList = new ArrayList<ClassA>();
ClassA a = new ClassA();
ClassA b = new ClassA();
ClassA c = new ClassA();
myList.add(a);
myList.add(b);
myList.add(c);
for (String inList : myList) {
System.out.println(inList);
}
}
}

I thought this would print

This is ClassA
This is ClassA
This is ClassA


Error
ClassB.java:11: incompatible types
found : ClassA
required: java.lang.String
for (String inList : myList) {

[Phil Dixon]

Changed this line to

 
for (Object inList : myList)
 
  

And now get

ClassA@82ba41
ClassA@923e30
ClassA@130c19b

[Julien Grenier]

for (String inList : myList) {
System.out.println(inList);
}

Error
ClassB.java:11: incompatible types
found : ClassA
required: java.lang.String
for (String inList : myList) { ...

Well as you can see in the error message it says found ClassA required String for (String inList : myList).

So the code

for (String inList : myList)

state that in the List called myList each element will be a String But this is not true because it is declared as a ArrayList of ClassA :

ArrayList<ClassA> myList

.

In conclusion the solution is to do :

for (ClassA inList : myList) { ...  

as the compiler told you.

[Tommy Becker]

Note that you're printing "This is ClassA" from the constructor of ClassA. This code as written should indeed print "This is ClassA" 3 times, but it's not working the way I think you think it's working. Think about what is actually happening when you say System.out.println(inList). . .