# 1.15 String Manipulation

**Suggested Skills:** 2.C, 3.C, 4.A, 4.B

**LO 1.15.A** — Develop code to create string objects and determine the result of creating and combining strings.

* **1.15.A.1** — A `String` object represents a sequence of characters and can be created by using a string literal or by calling the `String` class constructor.
* **1.15.A.2** — The `String` class is part of the `java.lang` package. Classes in the `java.lang` package are available by default.
* **1.15.A.3** — A `String` object is **immutable**, meaning once a `String` object is created, its attributes cannot be changed. Methods called on a `String` object do not change the content of the `String` object.
* **1.15.A.4** — Two `String` objects can be **concatenated** together or combined using the `+` or `+=` operator, resulting in a new `String` object. A primitive value can be concatenated with a `String` object. This causes the implicit conversion of the primitive value to a `String` object.
* **1.15.A.5** — A `String` object can be concatenated with any object, which implicitly calls the object's `toString` method (a behavior guaranteed to exist by the inheritance relationship every class has with the `Object` class). An object's `toString` method returns a string value representing the object. Subclasses of `Object` often override the `toString` method with class-specific implementation. **Method overriding** occurs when a public method in a subclass has the same method signature as a public method in the superclass, but the behavior of the method is specific to the subclass.
  * ❌ **EXCLUSION** — Overriding the `toString` method of a class is outside scope.

**LO 1.15.B** — Develop code to call methods on string objects and determine the result of calling these methods.

* **1.15.B.1** — A `String` object has index values from `0` to one less than the length of the string. Attempting to access indices outside this range will result in a `StringIndexOutOfBoundsException`.
* **1.15.B.2** — The following `String` methods are part of the Java Quick Reference:
  * `int length()` — returns the number of characters in a `String` object.
  * `String substring(int from, int to)` — returns the substring beginning at index `from` and ending at index `to - 1`.
  * `String substring(int from)` — returns `substring(from, length())`.
  * `int indexOf(String str)` — returns the index of the first occurrence of `str`; returns `-1` if not found.
  * `boolean equals(Object other)` — returns `true` if `this` corresponds to the same sequence of characters as `other`; returns `false` otherwise.
  * `int compareTo(String other)` — returns a value `< 0` if `this` is less than `other`; returns zero if `this` is equal to `other`; returns a value `> 0` if `this` is greater than `other`. Strings are ordered based upon the alphabet.
  * ❌ **EXCLUSION** — Using the `equals` method to compare one `String` object with an object of a type other than `String` is outside scope.
* **1.15.B.3** — A string identical to the single element substring at position `index` can be created by calling `substring(index, index + 1)`.

> 📘 **Lab:** After completing this unit, students will have covered all of the necessary content for the **Receipt Lab**.