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AP® Computer Science A · Unit 1 · Topic 1.2

Variables and Data Types: Checklist (Computer Science A 1.2)

A self-check list for data types, int, double, boolean, String and variable declarations, linked to the guide sections and practice questions.

Work through the list without notes. If you cannot do a statement, follow its link, then come back. Guide = study guide; Practice = practice questions.

Understanding

  • I can define a data type as a set of values with the operations on them. (Guide: “Storing information needs a plan”)
  • I can sort types into primitive and reference, and name the three primitive types of the course. (Guide: the table of types; Practice Question 1)
  • I can explain that a variable has a name, a fixed type and a value that can change. (Guide: “Variables: named storage that can change”)
  • I can explain the difference between 4 and 4.0 and why they have different types. (Guide: “Why int and double are different”; Practice Question 5)
  • I can explain that a String variable holds a reference to an object because String is a class. (Guide: the table of types; Practice Question 1)

Skills

  • I can choose int, double, boolean or String for a described piece of data. (Guide: Worked example 1; Practice Questions 2 and 7)
  • I can write a declaration with and without an initial value, and later change the value without repeating the type. (Guide: “Declaring a variable”)
  • I can say whether a declaration compiles and, if not, state why. (Guide: Worked example 2; Practice Questions 3 and 8)
  • I can trace declarations and assignments in a table and state the printed output. (Practice Questions 4 and 9)
  • I can write valid variable names following Java’s rules. (Guide: “Naming rules and habits”; Practice Questions 3, 6 and 8)

Reasoning

  • I can explain why a double cannot be stored in an int variable but an int can be stored in a double. (Guide: “The compiler checks types”; Practice Question 3)
  • I can explain why double avg = 7 / 2; holds 3.0 and not 3.5. (Guide: Worked example 2; Practice Question 5)
  • I can explain that assigning one primitive variable to another copies the value, so later changes do not affect the copy. (Guide: Worked example 2; Practice Questions 4 and 9)

All ticked? Move on to the Topic 1.3 study guide, Expressions and Output, or return to the course roadmap.

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