- Things in the real world
usually have
many different properties
- Example:
some properties of a student
- Student ID: an integer
- Name: a string
- Major: a string
- Level: an integer (1 = Freshman, 2 = Sophomore, 3 = Junior, 4 = Senior)
- To represent the
student ID of
a number of students,
we can use an
array of int
- To represent the
name of
a number of students,
we can use an separate
array of String
- To represent the
major of
a number of students,
we can use an separate
array of String
- To represent the
level of
a number of students,
we can use an separate
array of int
- Furthermore:
- We make certain that:
- The student ID in the ith array element of the student ID array
- The name in the ith array element of the name array
- The major in the ith array element of the major array
- The level in the ith array element of the level array
belong to the same student !!!
- We make certain that:
- Example: information on 3 students
- 314, John Doe, Math, 3 (Junior)
- 123, Mary Jane, Psych, 1 (Freshman)
- 876, Peter Pan, Chem, 2 (Sophomore)
stored in 4 arrays as follows:
studID[0] = 314 name[0] = "John Doe" major[0] = "Math" level[0] = 3 studID[1] = 123 name[1] = "Mary Jane" major[1] = "Psych" level[1] = 1 studID[2] = 876 name[2] = "Peter Pan" major[2] = "Chem" level[2] = 2
Multiple arrays where the elements are "synchronized" to represent information of the same item are called:
- Parallel arrays
- In computing, a
parallel array is a data structure
for representing
arrays of records.
Values located at the same index in each array are implicitly the fields of the same record.
Wikipedia page: click here
- Example: using parallel arrays
to represent student information
public class ParallelArray1 { public static void main(String[] args) { int[] studID = {314, 123, 876}; String[] name = {"John Doe", "Mary Jane", "Peter Pan"}; String[] major = {"Math", "Psych", "Chem"}; int[] level = {3, 1, 2}; /* ---------------------------------------------- Print the information in the parallel arrays ---------------------------------------------- */ for ( int i = 0; i < studID.length; i++ ) { System.out.print( studID[i] + "\t"); // \t = tab character System.out.print( name[i] + "\t"); System.out.print( major[i] + "\t"); System.out.print( level[i] ); System.out.println(); } } }
- Example Program:
(Demo above code)
- Prog file: click here
How to run the program:
- Right click on link and
save in a scratch directory
- To compile: javac ParallelArray1.java
- To run: java ParallelArray1
- Parallel arrays is
not commonly used
in modern programming languages
- Today, we use
array of user-defined type (class)
instead of
parallel arrays
- We will study user-defined types (classes) soon.