Array of the type `String`

Introduction
- We have seen many examples of:
- Array of other data types can be defined using very similar syntax as that used in arrays of double.
- In this webpage, we will show you the syntax used to define and access arrays of Strings

Previously discussed: defining and using an array of double

Syntax to define an array of double:

Step 1: double[] a; // The type "double[]" is the // "array object reference" type // The variable a contains an address of // an array of doubles
Step 2: a = new double[5] ; // new double[5] creates an array // of 5 elements of double type // The array elements are named: // a[0], a[1], a[2], a[3], a[4] // Each element is of the type double

Important facts:

An individual array element of the array a is is accessed using the syntax:
An individual array element of the array double a is a variable of the data type double:
Conclusion:

Now let us extrapolate these fact to an array of String
(And we will have learned how to define/access arrays of String)

Defining an array of String

Syntax to define an array of String:

Step 1: String[] a; // The type "String[]" is the // "array object reference" type // The variable a contains an address of // an array of Strings
Step 2: a = new String[5] ; // new String[5] creates an array // of 5 elements of String type // The array elements are named: // a[0], a[1], a[2], a[3], a[4] // Each element is of the type String

Using an array of String

Previously discussed: using a String typed variables (See: click here)

public class String01 { public static void main(String[] args) { String x; x = "Hello World"; // Assign to a String typed variable System.out.println(x); // Print a String typed variable } }

Now apply the fact: Each array element a[i] is a String typed variable !!!

Since each String array element is a String typed variable, we can conclude from the above example:

How to assign and print a String array element a[0]:

a[0] = "Hello World"; // Assign to a String array element System.out.println( a[0] ); // Print a String array element

Example program using String array:

public class String1 { public static void main(String[] args) { /* ------------------------------------- Create a String array of 5 elements ------------------------------------- */ String[] a; a = new String[5]; /* ------------------------------------- Assign a string to each array element ------------------------------------- */ a[0] = "Hello"; a[1] = "World"; a[2] = "How"; a[3] = "are"; a[4] = "you"; /* --------------------------------------------- Print the array elements (with a for loop) --------------------------------------------- */ int i; for ( i = 0; i < a.length; i++ ) { System.out.print( a[i] + " "); } System.out.println(); } }

Example Program: (Demo above code)
- Prog file: click here
How to run the program:
Output of this program:

Internal representation of array of String

The internal representation of an array of String is a bit complicated
But is it not crucial that you know the internal representation
In fact, when we use variables in the Java's library, we often do not know (nor care to know) the internal representaion

Consider the previous Java program:

For the curious student, the following diagram depicts - step-by-step - what happens in the above program:
Note:

Reading in a text file and store the words in an array of String

Problem description:

Write a program that reads in a text file (file containing words)
Store each word in the file (separately) in an element of an array of String.
Store the number of words in the input file in the variable numWords.
You can assume that the file contains at most 100 words.

Example:

Input file contains:

The array of String will contains:

numWords = 5 a[0] = "Hello" a[1] = "World" a[2] = "How" a[3] = "are" a[4] = "you" a[5] = NULL a[6] = NULL .... a[99] = NULL

Previously discussed: Read from a data file (see: click here )

Construct a Scanner object using an opened file:

/* --------------------------------- Open a data file --------------------------------- */ File myFile; // Define a "File" type variable to receive // the opened file myFile = new File("Path-name-of-the-file"); // Open the file /* -------------------------------------------------- Construct a Scanner from the opened file "myFile" -------------------------------------------------- */ Scanner in; // Define a Scanner typed variable in = new Scanner(myFile); // Construct a Scanner that read // data from opened file"myFile"

From this point onwards, you can use

in.nextDouble() to read a floating point number from the data file
in.nextInt() to read an integer number from the data file
in.next() to read a string (word) from the data file

Previously discussed: print the content of a (numeric) data file (see: click here )

Rough algorithm:

Open the file "inp1" Construct a Scanner object using the opened file as long as ( there is data in the Scanner object ) { read a word from the Scanner object; print the word; }

Java program:

import java.io.*; import java.util.Scanner; public class File01 { public static void main(String[] args) throws IOException { File myFile = new File("inp1"); // Open file "inp1" Scanner in = new Scanner(myFile); // Make Scanner obj with opened file String x; // Variable to receive a string while ( in.hasNext() ) { x = in.next(); // Read a string (word) System.out.println(x); // Print string read } System.out.println("Done"); } }

Rough algorithm for reading in words from files into an array of String:

a = String array of 100 elements; int numWords = 0; Open the file "inp1" Construct a Scanner object using the opened file as long as ( there is data in the Scanner object ) { a[numWords] = read next word from the Scanner object; numWords++; // Use the NEXT element in array to store // the next word in file ! } /* -------------------------------------------------------------- We can process the words in the array here if we so desire... -------------------------------------------------------------- */ ... (further array processing) ...

Java program:

import java.io.*; import java.util.Scanner; public class ReadText1 { public static void main(String[] args) throws IOException { String[] a = new String[100]; // Create String array of 100 elem's int numWords; // Count # words in input File myFile = new File("inp1"); // Open file "inp1" Scanner in = new Scanner(myFile); // Make Scanner obj with opened file numWords = 0; while ( in.hasNext() ) { a[numWords] = in.next(); // Read next string (word) numWords++; // Count # words AND use next // array element for next word } System.out.println("Printing the array..."); for ( int i = 0; i < numWords; i++ ) System.out.println( a[i] ); } }

Example Program: (Demo above code)
- Prog file: click here
- Input data file: click here
How to run the program:

Advanced Java/C programming trick

Advanced Java/C programmers write this loop:

while ( in.hasNext() ) { a[numWords] = in.next(); // Read next string (word) numWords++; // Count # words AND use next // array element for next word }

as follows:

while ( in.hasNext() ) { a[numWords++] = in.next(); }

(because numWords++ evaluates to the old value of numWords).

Array of the type String

Array of the type `String`