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4.11. Strings - Summary

In this chapter you learned about strings which are objects of the String class. Strings hold characters in a sequence. You learned the String methods that you will be expected to know on the exam. You were also introduced to concept of inheritance since the String class inherits from the Object class.

4.11.1. Concept Summary

  • append - One string can be appended to another using the + operator. This will create a new string with all the characters in the first string followed by all the characters in the second string.

  • child class - A class in Java can inherit object fields and methods from a parent class. The String class is a child class of the Object class.

  • concatenate - One string can be concatenated after another which is the same as appending one string after another.

  • immutable - Means that something doesn’t change. Strings are immutable. Any method that seems to change a string actually creates a new string.

  • index - A number that represents the position of a character in a string. The first character in a string is at index 0.

  • length - The number of characters in a string.

  • override - A child class can provide the same method as one it inherits from a parent class and in that case the child method will execute instead of the parent method. The child method overrides the parent method.

  • parent class - A class in Java has a parent class and it inherits object fields and public methods from the parent class. The Object class is the parent class of the String class.

  • reference - A reference is a way to find an object in memory. A reference is similar to a package tracking number since it helps you find the package.

  • string - A string is an object of the String class which holds sequences of characters. The String class also defines methods that you can execute on a string object like getting its length or getting a substring (copy of part of the string). Notice that the String class starts with an uppercase letter. All class names in Java start with an uppercase letter.

  • substring - A new string that contains a copy of part of the original string.

4.11.2. Java Keyword Summary

  • new - used to create a new object of a class.

  • null - used to indicate that an object reference doesn’t refer to any object yet.

4.11.3. Method Summary

  • str1.compareTo(str2) - returns 0 if they two strings have the same characters, a negative number if str1 is less than str2 and a positive number otherwise.

  • str1.length() - returns the number of characters in a string object including any spaces or special characters.

  • str1.equals(str2) - this method of the String class will return true if the characters in the two strings are the same.

  • str1.indexOf(str2) - returns the position that str2 starts in str1 or -1 if str2 isn’t in str1.

  • str1.substring(start,end) - returns a new string with all the characters in str1 from start to end - 1.

  • str1.toLowerCase() - returns a new string with the same characters as in str1, but all lowercase.

  • str1.toUpperCase() - returns a new string with the same characters as in str1, but all uppercase.

  • toString(obj) - this is a method that all classes inherit from the Object class. It can be overriden to print out a string representation of an object.

4.11.4. Practice

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