String comparison with logical operator in Java

Question

When comparing two strings, I was taught that we shouldn\'t use the logical operator (==). We should use String.equals(String) for the comparison. However, I see that the fo

Answer 1

The magic is called interning.

Java interns String literals and so there is a high probability that it evaluates to true:

String a = "hello";       // "hello" is assigned *and* interned
String b = "hello";       // b gets a reference to the interned literal
if (a == b)
   System.out.println("internd.");

String c = "hello" + Math.abs(1.0);   // result String is not interned
String d = "hello" + Math.abs(1.0);   // result String is not interned
System.out.println(c==d);             // prints "false"

c = c.intern();
System.out.println(c==d);             // prints "false"

d = d.intern();
System.out.println(c==d);             // prints "true"