Initialisation, Parameters and Scanner Input Methods in Java with Input Tracing (ICSE Class 9)

Understand Initialisation, Parameters and Scanner Input Methods with Input Tracing

Initialisation, Parameters and Scanner Input Methods with Input Tracing: key facts

Three ways

Initialisation	values in the code
Parameters	values passed at the call
Input stream	values typed during execution

Compare them by when the data arrives.

Scanner methods

• •nextInt() int
• •nextDouble() double
• •next() word
• •nextLine() line
• •next().charAt(0) char

There is no nextChar().

Line trap

nextInt() leaves the Enter | the next nextLine() reads an empty string

Read the text first or add an extra nextLine().

Initialisation, Parameters and Scanner Input Methods with Input Tracing 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 Initialisation, Parameters and Scanner Input Methods with Input Tracing

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

• No nextChar

  To read a character use next().charAt(0).

  Use it when: Reading a char.

• Next stops at a space

  next() reads one word; nextLine() reads the whole line.

  Use it when: Choosing a string method.

• Number, then line, trouble

  nextInt() then nextLine() reads an empty line.

  Use it when: The classic trap.

Initialisation, Parameters and Scanner Input Methods with Input Tracing: solved examples

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

12 7.5 Amit Rao
Delhi

int a = sc.nextInt();
double d = sc.nextDouble();
String w = sc.next();
String rest = sc.nextLine();
String city = sc.nextLine();
System.out.println(a + "|" + d + "|" + w + "|" + rest + "|" + city);

int n = sc.nextInt();
String s = sc.nextLine();
String s2 = sc.nextLine();
System.out.println(n + " [" + s + "] " + s2);

int total = 100;
obj.show(7, 3);
int marks = sc.nextInt();

char c = sc.next().charAt(0);
System.out.println(c + " " + (int) c);

Where students lose marks in Initialisation, Parameters and Scanner Input Methods with Input Tracing

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

• ✗Mistake: Using a non-existent nextChar()

  Other languages are remembered.

  Wrong working

  char c = sc.nextChar();

  Right working

  char c = sc.next().charAt(0);

  ✓Do this: Scanner has no nextChar().

  Usually costs: 1 mark

• ✗Mistake: nextLine() straight after nextInt()

  The leftover Enter is forgotten.

  Wrong working

  The name is always empty

  Right working

  Read the text first or add an extra sc.nextLine();

  ✓Do this: Remember the leftover Enter.

  Usually costs: 2 marks

• ✗Mistake: Wrong method for a decimal

  Type and method differ.

  Wrong working

  double x = sc.nextInt();

  Right working

  double x = sc.nextDouble();

  ✓Do this: Use the matching method.

  Usually costs: 1 mark

Practice questions on Initialisation, Parameters and Scanner Input Methods with Input Tracing

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 method reads a single word from the input?
   (a) nextLine() (b) next() (c) nextInt() (d) charAt()

   Hint

   It stops at a space.

   Answer

   (b) next()

2. Q2 · 2 marks · Very short answerBoard level

   Write statements to read a full name that may contain spaces and then an age as an int.

   Hint

   Read the text first.

   Answer

   Scanner sc = new Scanner(System.in);
   String name = sc.nextLine();
   int age = sc.nextInt();

3. Q3 · 2 marks · Very short answerHarder board level

   Name the Scanner method that reads each: (i) 12 (ii) 12.5 (iii) the letter Q (iv) the text New Delhi.

   Hint

   Match the type.

   Answer

   (i) nextInt() (ii) nextDouble() (iii) next().charAt(0) (iv) nextLine()

4. Q4 · 3 marks · Short answerHarder board level

   The input is 5 6. Find the output:

   int a = sc.nextInt();
   int b = sc.nextInt();
   System.out.println(a + b + " " + a + b);

   Hint

   The first + adds numbers; later ones join.

   Answer

   11 56 (a + b = 11 is added first; then " " is joined, then 5 and 6 are joined as text)

5. Q5 · 3 marks · Short answerHOTS / competency

   A program reads String name = sc.next(); and for the input Mary Ann it prints only Mary. Explain and correct.

   Hint

   Where does next() stop?

   Answer

   next() stops at the first space, so only Mary is read. Use String name = sc.nextLine(); to read the whole line (and read it before any number).

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.Which method reads a float?Show answer

   nextFloat()

2. 2.Which call gives a char?Show answer

   next().charAt(0)

3. 3.Which method reads a whole line?Show answer

   nextLine()

4. 4.Which method reads one word?Show answer

   next()

5. 5.What are the three ways of supplying data?Show answer

   Initialisation, parameters and input stream.

6. 6.Does nextInt() consume the Enter?Show answer

   No.

Initialisation, Parameters and Scanner Input Methods with Input Tracing: frequently asked questions