Java Structure, Identifiers, Data Types and Variables: ICSE Class 8

Understand Java Program Structure, Identifiers, Data Types and Variables

class Welcome
{
    public static void main(String args[])
    {
        System.out.println("Welcome to Java");
        System.out.println("I am in Class 8");
    }
}

Java Program Structure, Identifiers, Data Types and Variables: key facts

Identifier rules

• •Letters, digits, underscore and dollar sign
• •Not start with a digit
• •No spaces
• •Not a keyword
• •Case-sensitive

2marks is invalid; marks2 is valid.

Data types

int	whole numbers
float and double	decimals
char	one character
boolean	true or false
String	text

float needs f after the literal.

Errors

Syntax error: found at compile time | Logical error: wrong answer found by testing

A missing semicolon is a syntax error.

How to answer Java Program Structure, Identifiers, Data Types and Variables questions

1. 1Check each identifier against the five naming rules.
2. 2Choose the data type from the value: whole, decimal, one character, text or true or false.
3. 3Declare and initialise with the correct literal form (f, single quotes, double quotes).
4. 4Trace the printed output line by line.
5. 5Classify any error as syntax or logical.

Java Program Structure, Identifiers, Data Types and Variables in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Tricks to remember Java Program Structure, Identifiers, Data Types and Variables

Short memory aids. Say each one aloud once, then use it on a question the same day.

• 2marks no, marks2 yes

  An identifier cannot start with a digit.

  Use it when: Naming rules.

• Quotes tell the type

  Single quotes: char; double quotes: String.

  Use it when: Literals.

Java Program Structure, Identifiers, Data Types and Variables: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

int age = 13;
String name = "Riya";
char grade = 'A';
System.out.println("Name: " + name);
System.out.println("Age: " + age);
System.out.println("Grade: " + grade);

class Test
{
    public static void main(String args[])
    {
        int 2age = 14
        System.out.Println(2age);
    }
}

Where students lose marks in Java Program Structure, Identifiers, Data Types and Variables

The slips examiners see most often, and what to write instead.

• ✗Mistake: Using a digit to start a name

  Identifiers cannot start with a digit.

  Wrong working

  int 2age;

  Right working

  int age2;

  ✓Do this: Check rule 2.

  Usually costs: 1 mark

• ✗Mistake: Writing a float without f

  Decimals are doubles by default.

  Wrong working

  float h = 152.5;

  Right working

  float h = 152.5f;

  ✓Do this: Add f or use double.

  Usually costs: 1 mark

• ✗Mistake: Using wrong quotes

  Single quotes are for char, double quotes for String.

  Wrong working

  String name = 'Riya';

  Right working

  String name = "Riya";

  ✓Do this: Match quotes to type.

  Usually costs: 1 mark

Practice questions on Java Program Structure, Identifiers, Data Types and Variables

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   Which declaration correctly stores the text Class 8?
   (a) char t = "Class 8"; (b) String t = "Class 8"; (c) int t = "Class 8"; (d) boolean t = "Class 8";

   Hint

   Text in double quotes needs a class type.

   Answer

   (b) String t = "Class 8";

2. Q2 · 2 marks · Short answerBoard level

   State four rules for naming an identifier in Java. (2 marks)

   Hint

   Digits, spaces, keywords, case.

   Answer

   It may use letters, digits, underscore and $; it must not start with a digit; it must not contain spaces; it must not be a keyword; it is case-sensitive.

3. Q3 · 3 marks · Short answerHarder board level

   Write the output of: int a = 17, b = 5; System.out.println("Sum = " + a + b); (3 marks)

   Hint

   Text first, so numbers are joined as text.

   Answer

   Sum = 175, because after the text each number is joined as text. With brackets (a + b) the output would be Sum = 22.

4. Q4 · 4 marks · Long answerHarder board level

   Declare variables to store a book title, number of pages, price with paise and whether it is available. Give a one-line reason for each type. (4 marks)

   Hint

   Four types.

   Answer

   String title; (text). int pages; (whole number). double price; (decimal). boolean available; (true or false).

5. Q5 · 4 marks · Long answerHOTS / competency

   One program finds the area of a rectangle with + instead of *, and another leaves out a semicolon. Classify each error, say when it is found and how it is corrected. (4 marks)

   Hint

   Compiler versus testing.

   Answer

   Leaving out the semicolon is a syntax error; the compiler reports it when compiling and it is corrected by adding the semicolon. Using + instead of * is a logical error; the program runs but gives a wrong area, so it is found only by testing with sample data and corrected by using * in the formula.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Where does a Java program start running?Show answer

   In the main method.

2. 2.Which tool turns source code into bytecode?Show answer

   The compiler.

3. 3.What runs bytecode?Show answer

   The Java Virtual Machine.

4. 4.Is Age the same as age?Show answer

   No, Java is case-sensitive.

5. 5.What does println do?Show answer

   Prints and moves to a new line.

6. 6.Which type holds true or false?Show answer

   boolean.

Java Program Structure, Identifiers, Data Types and Variables: frequently asked questions