Creating Strings

Creating Strings

1. What Is a String? (beginner)

String = sequence of chars (object, not primitive!). Lives in java.lang (no import). Immutable (can't change — new object each edit!). Two ways to create.

2. Two Ways (exam must-know!)

String s1 = "hello";              // literal (goes to String Pool — reused!)
String s2 = new String("hello");  // new object on Heap (fresh copy!)
String s3 = "hel" + "lo";         // + joins at compile time → "hello"
char[] ch = {'h','i'};
String s4 = new String(ch);       // from char array → "hi"
String s5 = "";                   // empty (length 0, NOT null!)
String s6 = null;                 // no object! (s6.length() → crash!)

Pool diagram: s1 and "hello" literal share ONE pooled object; s2 is a separate Heap copy.

3. Beginner Code — Pool Proof

String a = "hi";
String b = "hi";
String c = new String("hi");
System.out.println(a == b);      // true (same pooled object!)
System.out.println(a == c);      // false (different objects!)
System.out.println(a.equals(c)); // true (same CONTENT — use this!)

4. Traps

• == compares addresses (pool accident!), .equals() compares content (always use!).
• null String + method → NullPointerException. Empty "" is safe (length 0).
• + in loop creates garbage (many objects!) — use StringBuilder (later topic).

5. Exam Points

• Two ways + pool diagram — 5-7 marks, very frequent.
• == vs .equals() proof — 5 marks, all-time favourite.