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mrahmedcomputing

KS3, GCSE, A-Level Computing Resources

Lesson 5. String Handling and Type Casting

Lesson Objective

  • Understand how to manipulate Strings in Java using the following methods:
    • .length()
    • .substring
    • .indexOf
    • .charAt()
    • .toUpperCase()
    • .toLowerCase()
    • String Concatenation
  • Be able to type cast from one data type to another.

Lesson Notes

Indexing

To access a single item in an array, you refer to its index position. Each item is assigned a number, and the first item is denoted as position "0".

To extract one item from a string, you would refer to its index position. Like and Array, each item is given a number. The first item is referred to as position "0".

.Length()

The length of a String can be found with the length() method:

Code:

public class Hello_World_1 {
   public static void main(String args[]){ 
      String alp = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
      System.out.println("Length of the string is ") 
      System.out.println(alp.length());
   }
}
// NOTE:
// .Length() is used for Strings
// .Length is used for Arrays

Cmd Output:

Length of the string is:
26

.indexOf

The indexOf() method is used to find the index of a character or substring within a string. It returns the position of the first occurrence of the specified character or substring. If the character or substring is not found, it returns -1.

Code:

public class Hello_World_1 {
   public static void main(String args[]){ 
      String sub = "Computer Science is the best";
      System.out.println(sub.indexOf("r"));
      System.out.println(sub.indexOf("Science"));
      
      System.out.println(sub.indexOf("e", 7));
   }
}
// Look for “e” starting from position 7.

Cmd Output:

7
9
12

.charAt()

The charAt() method returns the character at the specified index positions in a string.

Code:

public class Hello_World_1 {
   public static void main(String args[]){ 
      String sub = "Computer Science is the best";
      System.out.println(sub.charAt(2));
      System.out.println(sub.charAt(sub.length-1));
   }
}

Cmd Output:

m
t

.substring()

Returns a new string which is the substring of a specified string.

Code:

public class Hello_World_1 {
   public static void main(String args[]){ 
      String sub = "Computer Science is the best";
      System.out.println(sub.substring(24));
      System.out.println(sub.substring(9,15));
   }
}
// Starts from position 24 and returns all following characters
// Starts from position 9 and returns all characters up to 15

Cmd Output:

best
Science

String Concatenation

The “+” operator can be used between strings to join them together. This is called concatenation.

Code:

public class Hello_World_1 {
   public static void main(String args[]){ 
      String a = "Computer";
      String b = "Science";
      System.out.println(a + " " + b); 
   }
}
// Note that we have added an empty text (" ") to create a space between firstName and lastName on print.
// You can also use the concat() method to concatenate two strings:
// System.out.println(a.concat(b));

Cmd Output:

Computer Science

WARNING:

Java uses the + operator for both addition and concatenation. Numbers are added. Strings are concatenated. If you add a number and a string, the result will be a string concatenation.

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