How Many Objects Does `String a = "abc"` Actually Create in Java?

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 instance; otherwise the literal is added to the pool and a points to it.

// When "abc" is not in the constant pool
// 1) three char values 'a','b','c' are created on the stack
// 2) a new String object is created on the heap using those chars
// 3) that 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 and a points to it; the newly created object also references the literal in the constant pool.

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);

Output: true, false, false. The `new String("abc")` expression 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.