Summary: Using Classes and Objects

In this lesson, we will look the important points we covered in this chapter.

  • The Java Class Library, which contains a collection of standard classes that we can use in our programs, is organized into packages of classes.
  • We use the operator new to create a new object of a class type.
  • A variable of a primitive data type contains the actual value of the data it represents. A variable of a class type contains a reference to the object that it represents.
  • Characters within strings are represented by Unicode values.
  • Certain escape characters are written as two characters. For example, the new-line character is \n.
  • Methods within the class String enable us to manipulate strings. For example, we can join two strings end to end, get the length of a string, get the character at a certain position, locate a substring, and compare strings.
  • We can use the class Scanner to extract tokens from a string that is either defined in our program or read as data. By default, white space separates the tokens, but we can define other characters as delimiters.
  • An object of the class LocalTime represents the time that it was created. We can compare two such objects and decide which one represents the earlier time.
  • The class BigDecimal provides accurate decimal arithmetic with arbitrarily large numbers.
  • A wrapper class such as Integer represents primitive data as an object. Integer contains the method parseInt that converts a string containing an integer to an int. It also defines constants that represent the minimum and maximum values of an int value.
  • The class Random has methods to generate numbers that appear to be random.
  • The class DecimalFormat enables us to format the output of a real number or an integer according to a pattern that we create.

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