2.1. Worked Example: Create Instance of Scanner

Subgoals for using objects (creating instances)

  1. Declare variable of appropriate class datatype.

  2. Assign to variable: keyword new, followed by class name, followed by ().

  3. Determine whether parameter(s) are appropriate (API)

    1. Number of parameters

    2. Data types of the parameters

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SG1: Declare variable of appropriate class datatype.

In the code block below, the variable name sysinScanner was selected to better describe what we are going to do with this Scanner, which will become more clear in SG3.

Scanner sysinScanner;

SG2: Assign to variable:  keyword new, followed by class name, followed by ().

sysinScanner = new Scanner();

SG3: Determine whether parameter(s) are appropriate (API)

The figure below shows the Java documentation, so we can determine what parameter(s) we need. Most of the ways to construct a Scanner require exactly 1 parameter, an object that represents the source of input data. We’ll use the standard system input from the console System.in.

API docs for Scanner constructor

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