Java Programming

I thought that strings that are equal would always refer to the same object. The following code seem to suggest that is not the case

class ScjpTest{
	
	public static void main(String[] args){
	
		String a = "Hello";
		String b = "World";

		String c = a + "World";
		String d = "HellowWorld";

		String e = a.concat("World");

		System.out.println("d==c : " + d==c);
		System.out.println("d==e : " + d==e);
		
		
	}
}

output

false
false