What is the difference between String a; and String a = new String ();

Answer 1, authority 100%

According to @Pavel Parshin , in the first case the variable a is not initialized (it is not even equal to null ). Its further use is impossible, otherwise a compilation error will occur error: variable a might not have been initialized . Example .

In the second case, according to en-SO , a new String object is created with an empty line inside ""

Sting a;
TextUtils.isEmpty (a); // compilation error - the variable is not initialized.
a = new String ();
TextUtils.isEmpty (a); // true

Answer 2, authority 42%

The above are good answers, but if it’s not clear, then String is the name of the class, String a; is the creation of a pointer to a class variable String , it tells us that the variable of this class will be available at this pointer, but so far it is only a pointer that does not point to anything specific. new String () is the creation of a specific object in memory, for which space is allocated, and to which the same pointer a can be used, thus this construction is String a = new String (); tells us that the pointer a will point to this particular object in memory new String () .

Answer 3, authority 8%

When writing String b – you just create a variable b , which is a reference to an object of type string (but so far it is not does not indicate).

When you write String b = "Hello world" , you initialize the object immediately, effectively substituting new . And assign our link b a link to this object.