How Many Objects Does a Java String Creation Actually Allocate?

1. String a = "abc" creates zero or one object. First a reference variable a is defined on the stack; the JVM checks the string constant pool for "abc". If it exists, a points to that pooled string; otherwise the literal is added to the pool and a points to it.

// When "abc" is not in the pool
// (1) three char values 'a','b','c' are created on the stack
// (2) a new String object is created on the heap from those chars
// (3) the String object is placed into the constant pool
// (4) a references the pooled object

String a = "abc";
// equivalent to
char data[] = {'a','b','c'};
String a = new String(data);

2. String a = new String("abc") creates one or two objects. A reference variable a is defined on the stack, then a new String object is allocated on the heap; a points to this object, which in turn references the pooled literal "abc".

3. Comparison

String a = "abc";
String b = "abc";
String c = new String("abc");
String d = new String("abc");
System.out.println(a == b);
System.out.println(a == c);
System.out.println(c == d);

Result: true, false, false. The expression new String("abc") always creates a new heap object regardless of the constant pool, so c and d refer to distinct objects, while a and b refer to the same pooled instance.