Looping through Set containing Entry objects - hashmap

Question

import java.util.*;
public class HelloWorld{
public static void main(String []args){
HashMap<Integer,String> h = new HashMap<Integer,String>();
h.put(100,"Hola");
h.put(101,"Hello");
h.put(102,"light");
System.out.println(h); // {100=Hola, 101=Hello, 102=light}
Set s = h.entrySet();
System.out.println(s); // [100=Hola, 101=Hello, 102=light]
for(Map.Entry<Integer,String> ent : s)
{
System.out.println("Key=" + ent.getKey() + " Value=" + ent.getValue());
}
}
}
Compile error
HelloWorld.java:13: error: incompatible types: Object cannot be converted to Entry<Integer,String>
for(Map.Entry<Integer,String> ent : s)
^
I am trying to print key-value pair for each entry type object in the Set s. But it gives compile time error shown above. But code works fine if I replace "s" with " h.entrySet()" and loops fine..How does using reference to hold "h.entrySet()" cause compile error ?

Answer 1

The line
Set s = h.entrySet();
should be
Set<Map.Entry<Integer,String>> s = h.entrySet();
because for each loop below doesn't know what type of Set s is ?
This code works:
import java.util.*;
public class HelloWorld{
public static void main(String []args){
HashMap<Integer,String> h = new HashMap<Integer,String>();
h.put(100,"Hola");
h.put(101,"Hello");
h.put(102,"light");
System.out.println(h); // {100=Hola, 101=Hello, 102=light}
Set<Map.Entry<Integer,String>> s = h.entrySet();
System.out.println(s); // [100=Hola, 101=Hello, 102=light]
for(Map.Entry<Integer,String> ent : s)
{
System.out.println("Key=" + ent.getKey() + " Value=" + ent.getValue());
}
}
}
Whenever you see
incompatible types: Object cannot be converted to.. error
it means JVM is trying to covert Object type to some other type and it leads to compilation error . Here it's happening in the for loop.