String comparison (equals, compareTo) in Kotlin - Step-by-Step Execution

Concept Flow - String comparison (equals, compareTo)

Start

↓

Get two strings

↓

Use equals()

↓

Are strings exactly same?

Yes→Return true

↓

Return false

↓

Use compareTo()

↓

Compare lex order

↓

Return negative/zero/positive

↓

End

First, we check if two strings are exactly equal using equals(). Then, we compare their order lexicographically using compareTo(), which returns a number indicating their order.

Execution Sample

Kotlin

val a = "apple"
val b = "Apple"
println(a.equals(b))
println(a.compareTo(b))

This code compares two strings 'apple' and 'Apple' using equals() and compareTo(), printing the results.

Execution Table

Step	Action	Evaluation	Result
1	Assign a = "apple"	a = "apple"	a = "apple"
2	Assign b = "Apple"	b = "Apple"	b = "Apple"
3	Evaluate a.equals(b)	"apple".equals("Apple")	false
4	Evaluate a.compareTo(b)	"apple".compareTo("Apple")	32
5	Print equals result	false	Output: false
6	Print compareTo result	32	Output: 32

💡 All steps completed, program ends after printing results.

Variable Tracker

Variable	Start	After Step 1	After Step 2	Final
a	undefined	"apple"	"apple"	"apple"
b	undefined	undefined	"Apple"	"Apple"

Key Moments - 2 Insights

Why does equals() return false even though the words look similar?

equals() checks exact match including case. "apple" and "Apple" differ in uppercase 'A', so it returns false (see step 3 in execution_table).

What does the number 32 from compareTo() mean?

compareTo() returns a positive number because lowercase 'a' has a higher Unicode value than uppercase 'A'. The number 32 is the difference in their Unicode codes (see step 4).

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of a.equals(b) at step 3?

A true

B false

C null

D 32

💡 Hint

Check the 'Result' column at step 3 in execution_table.

At which step does the program print the compareTo() result?

A Step 4

B Step 5

C Step 6

D Step 3

💡 Hint

Look for the step where output shows 'Output: 32' in execution_table.

If we change b to "apple", what would a.equals(b) return?

A true

B 32

C false

D null

💡 Hint

Refer to how equals() works in key_moments and execution_table step 3.

Concept Snapshot

String comparison in Kotlin:
- Use equals() to check exact match (case-sensitive).
- Use compareTo() to get lexicographic order:
  returns 0 if equal,
  negative if first < second,
  positive if first > second.
- equals() returns Boolean, compareTo() returns Int.

Full Transcript

This example shows how Kotlin compares strings. First, two strings a and b are assigned values "apple" and "Apple". The equals() function checks if they are exactly the same, including case, and returns false because 'a' and 'A' differ. Then compareTo() compares their lexicographic order and returns 32, a positive number, because lowercase 'a' has a higher Unicode value than uppercase 'A'. The program prints false and 32 as results. This teaches that equals() is strict and case-sensitive, while compareTo() tells order by returning a number.