Does new String("Hello_42") == "Hello_" + 42?

Such questions about comparing string and numeric constants test understanding of the concept of literal pools. This should not be confused with the class's constant pool. The virtual machine reuses the same object for a string literal when loading a containing class if it has already been allocated in the heap. This is why "Hello" == "Hello" is true, despite the fact that String is a reference type. This optimization is possible thanks to the immutability of the String String class, and is known as string interning.

Besides literals themselves, interning is applied to all constant expressions. In this example, the implicit conversion of the number 42 to a string and the concatenation of constants are considered constant expressions. This makes "Hello_42" == "Hello_" + 42 true.

The literal pool does not work when the new operator is explicitly used. This is why the entire expression new String("Hello_42") == "Hello_" + 42 is false.