Variable Declarations

1. Must declare a variable (once) before using it
2. Form of a declaration:
1. type identifier;
2. type identifier, identifier, ...;
3. Convention - start identifier with lower case - indicate multiple words with uppercase letter
4. Form of a declaration:
1. String msg;
2. String messageOfTheDay, soupOfTheDay;

Assignment

1. Must always assign to a variable before using it!
2. Form of a assignment:
1. identifier = value;
3. left hand side (or LHS) refers to id
4. right hand side (or RHS) refers to value
5. variable must be declared, types must be consistent
6. LHS is used to store, while RHS used to retrieve
7. Examples:

String teamName;
PrintStream outputMonitor;
teamname = "Tigers";  // legal
outputMonitor = System.out;  // legal
teamName = System.out;  // illegal
teamName = outputMonitor;  // illegal
teamname = "The Clemson Tigers";  // legal
String s;
s = teamName;  // legal
String s;      // illegal
PrintSteam s;  // illegal

Assignment Changes Variables

1. Consider:

  String teamName = "Tigers";
  teamName = "Blue Devils";
  teamName = "Tar Heels";

2. Each assignment sets teamName to a new value.
3. Old references are gone.

Reference Variables and Objects

1. Reference variable refer to objects not reference variables!
2. Consider:

  String teamName = "Tigers";
  String name;
  name = teamName;

3. name and teamName refer to same object!

Variables are Independent

1. Reference variable refer to objects not reference variables!
2. Consider:

  String teamName = "Tigers";
  String name;
  name = teamName;
  teamName = "Clemson";
  name = teamName;

Ordering Statements - More than one way to skin a cat

1. Consider:

class Program2 {
        public static void main(String arg[]) {
                String          teamName;
                String          bigTeamName;
                teamName = "clemson tigers";
                bigTeamName = teamName.toUpperCase();
                System.out.println(teamName);
                System.out.println(bigTeamName);
        }
}

class Program2 {
        public static void main(String arg[]) {
                String          teamName;
                teamName = "clemson tigers";
                String          bigTeamName;
                bigTeamName = teamName.toUpperCase();
                System.out.println(teamName);
                System.out.println(bigTeamName);
        }
}

class Program2 {
        public static void main(String arg[])  {
                String          teamName = "clemson tigers";
                String          bigTeamName = teamName.toUpperCase();
                System.out.println(teamName);
                System.out.println(bigTeamName);
        }
}

More String Methods

1. Prototypes for String:

Method	Returns	Arguments	Description
toUpperCase	String	none	Creates uppercase version of given string
toLowerCase	String	none	Creates lowercase version of given string
length	a number	none	Length of given string
trim	String	none	Creates a string with leading and ending blanks removed
concat	String	String	Creates a string with given string concatenated to String object
substring	String	positions of first char and last char + 1	Creates a string that is substring of given string
substring	String	position of first char	Creates a string that is substring of given string starting at position of first char

2. Note - Strings are indexed by 0
3. substring is an overloaded method, i.e., class defines two methods with same method-name but different signatures

Cascading

• Message sent to object is returned by message and in turn message sent object returned by that message

    String firstName = "Robert";
    String lastName = "Martin";
    String yearBorn = "1956";
    String code;
    code = firstName.substring(0,2).concat (lastName).substring(0,4).concat (yearBorn);

Composition

• Return value of one message becomes argument for another.

    String firstName = "Robert";
    String lastName = "Martin";
    String yearBorn = "1956";
    String code;
    code = firstName.substring(0,2).concat (lastName.substring(0,2).concat (yearBorn);

Know Terminology and review at end of chapter