Working with String objects

String indexing and the charAt method

String name = "Brandon";
//             0123456

char letter = name.charAt(0);
System.out.println(letter);  // prints B

letter = name.charAt(2);
System.out.println(letter);  // prints a

letter = name.charAt(name.length() - 1);
System.out.println(letter);  // prints n

// Each of the lines below throws a StringIndexOutOfBoundsException.

letter = name.charAt(name.length());  // name.length() returns 7
letter = name.charAt(7);
letter = name.charAt(-1);

The characters in a String are indexed from 0 up to but not including the length.

The charAt method returns the character at the specified position in a String as a char. Working with char values demonstrates the char type.

Material covered on other site

String objects are used extensively on the AP CS A Exam. The pages linked below cover the parts of the String class featured on the AP CS A Exam.

Strings on the AP CS A Exam has demonstrations of these topics.

• Comparing String objects for equality using the equals method
• The length method
• Getting part of a String using the 2 substring methods
• Finding a String inside another String using the indexOf method
• Concatenating (putting together) String objects using the + and += operators, including converting other types
• String immutability

compareTo on the AP CS A Exam demonstrates how to compare String objects for order (see which comes first).

Converting a char into a String

char letter = 'a';
String str = "" + letter;

After this code segment, str stores a reference to "a" (a String).

String concatenation can be used to convert a char into a String. "" is the empty String. When at least 1 operand of the + operator is a String, the operator behaves as concatenation.

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