How compare strings in Java (in-depth examination)

There are two ways:

• == tests for reference equality
• .equals() tests for value equality

When using == operator for string comparison you are not comparing the contents of the string but are actually comparing the memory address, if they are both equal it will return true and false otherwise. 

Whereas equals in string compares the string contents.

Some examples:

// These two have the same value
new String("test").equals("test") // --> true 

// ... but they are not the same object
new String("test") == "test" // --> false 

// ... neither are these
new String("test") == new String("test") // --> false 

// ... but these are because literals are interned by 
// the compiler and thus refer to the same object
"test" == "test" // --> true 

// concatenation of string literals happens at compile time,
// also resulting in the same object
"test" == "te" + "st" // --> true

// but .substring() is invoked at runtime, generating distinct objects
"test" == "!test".substring(1) // --> false

// interned strings can also be recalled by calling .intern()
"test" == "!test".substring(1).intern() // --> true