Section 9.5 Forgetting to use the new keyword to create an object

Unlike Python, where you can create a new object without explicitly using a keyword, Java requires the new keyword to instantiate a new object.

Listing 9.5.1.

The error message in Listing 9.5.1 occurs when you forget to use the new keyword to instantiate an object. Specifically, on line 8 of Histo.java, data = Scanner(new File("test.dat")); leads to a ’cannot find symbol’ error. While the message states ’symbol: method Scanner(File)’, this can be misleading. Java incorrectly interprets Scanner() as an attempt to call a static method named Scanner within the Histo class (or an inherited one). However, Scanner is a constructor of the Scanner class, not a standalone method, and therefore requires the new keyword (e.g., data = new Scanner(new File("test.dat"));) to create a new Scanner object.

Checkpoint 9.5.2.

Based on Listing 9.5.1, select all of the statements that are true about creating objects in Java.

Java requires the new keyword to create a new object.
Correct! Unlike Python, Java needs the new keyword to instantiate an object.
Writing data = new Scanner(new File("test.dat")); would fix the error.
Correct! Adding new before Scanner properly creates the object and resolves the error.
Scanner is a constructor of the Scanner class, not a standalone method.
Correct! Because Scanner is a constructor, it must be called with new.
Java can create objects without a keyword, just like Python.
Incorrect. Unlike Python, Java requires the new keyword to instantiate objects.
The "cannot find symbol" error here means the Scanner class was not imported.
Incorrect. The Scanner class is imported; the error is caused by the missing new keyword.

You have attempted of activities on this page.

Prev Top Next