Java String Operations Flashcards (Weeks 3-6)

String Manipulation in Java

• String concatenation in Java uses the + operator.
• Method toUpperCase() converts all characters in a String to uppercase, e.g., "hello" becomes "HELLO".
• The length() method returns the number of characters in a String, e.g., "Grace Murray Hopper" has a length of 19.
• The method substring(startIndex, endIndex) extracts a portion of a String; for "Knowledge is power.", words.substring(4, 9) returns "ledge".
• Using replace(oldChar, newChar) modifies a String, as in the case of "Mississippi" to "Mwasswassippi" by replacing "is" with "was".
• The indexOf(char) method returns the index of the first occurrence of a character in a String, e.g., '3' in "123 Main Street" is at index 2.

Output Control

• To print special characters or formatted strings, escape sequences like \" are used. For example, System.out.println("\"Oom Pah Pah Oom Pah Pah,\" that's how it goes."); prints with quotation marks.
• Valid and invalid string literals include options with escape characters; option c ""\n"" is invalid.

Character Handling

• The escape sequence \t represents a horizontal tab, while \n denotes a newline character.
• Unicode escape sequences specify characters in hexadecimal format for non-ASCII characters. ASCII refers to a small character set primarily for English and symbols.
• Lexicographic ordering is the technique used to order characters based on a character set, which in Java is represented by Unicode.

Memory and Encoding

• Character encoding determines how characters are stored in memory, with supplementary characters representing those that don't fit into fixed-width encodings.
• Non-printable characters, such as newline, do not have visual symbols.

Java Package System

• The String class belongs to the java.lang package, which is auto-imported into every Java program.
• Classes can share names if they are in different packages; however, their fully qualified names do not always need to be used in the code.
• An import statement specifies which class to reference in a program and should be placed above the class definition.
• A static import allows direct access to static methods without needing to reference the class name.

Objects and Constructors

• The keyword new is an operator used to create new objects, and a class constructor has the same name as the class.
• Objects can be declared without being instantiated immediately. A null reference will raise an exception if accessed.
• A String object can indeed be created with the new operator, and String methods can also be called on String literals.

Control Flow

• Conditional statements evaluate expressions, e.g., if a total of 5 is compared in an if statement with a value of 8, it does not execute the inner statement, resulting in no output and continued processing.