String Methods

Main Ideas and Concepts

What strings are (Java)

• Strings are sequences of characters (e.g., STR = "hello").
• A string can be viewed like a list/array of characters, where each character has an index.
• Indexing starts at 0 (e.g., "hello" → h at 0, e at 1, …).

Strings are objects, not primitives

• Because strings are objects, compare string values using .equals(), not ==.
• To check whether two strings contain the same characters, use:
  • string1.equals(string2).

How to find documentation

• Documentation explains how to use methods and classes.
• You can use:
  • IDE documentation (e.g., a documentation tab)
  • Online documentation
• Suggested search method:
  • Search Google for: “Java” + class or method name
  • Example given: Java String (using the first relevant link)

Key String methods highlighted

• charAt(index): returns the character at the specified index.
• equals(...): compares whether two strings are equal (by content).
• equalsIgnoreCase(...): compares equality while ignoring case differences.
• indexOf(...): returns the index where a substring/string occurs.
• length(): returns the number of characters in the string.
• substring(...): returns part of a string:
  • substring(beginIndex) → rest of the string starting at beginIndex
  • substring(beginIndex, endIndex) → characters from beginIndex inclusive to endIndex **exclusive`

Important rule: strings are immutable

• Once created, a string cannot be changed.
• Methods like substring return a new string rather than modifying the original.

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Substring Indexing Lesson (Explicit Rule)

When calling substring(beginIndex, endIndex):

• beginIndex is inclusive (included in the result)
• endIndex is exclusive (not included in the result)

Example:

• If greeting = "good day", then:
  • greeting.substring(0, 4)
  • includes characters at indices 0..3.

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Method Usage Examples Demonstrated

• charAt example:

  • Given quote = "a long long time ago", quote.charAt(0) retrieves the character at index 0.

• substring example:

  • Given greeting = "good day", greeting.substring(0, 4) returns the portion starting at index 0 up to (but not including) index 4.

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Looping Over a String’s Characters (Procedure)

Goal

Print every character in a string on its own line.

Steps

1. Declare a string (example):
   • STR = "hello world"
2. Get its length:
   • int length = STR.length();
   • (example print) System.out.println(length);
3. Loop through indices and print each character:
   • Use a for loop:
     • for (int i = 0; i < STR.length(); i++)
   • Inside the loop:
     • char cur = STR.charAt(i);
     • System.out.println(cur);

This prints each character from the string on a separate line.

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Speakers / Sources Featured

• No specific speaker name is mentioned.
• Source referenced: the Java String class documentation (accessed via IDE documentation and/or Google).