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➗ Operators & Expressions · Beginner

Relational & equality operators in Java

<, >, <=, >=, ==, != and comparing references vs values.

🧩 The mysteryTwo Strings both say "cat", yet == says they're NOT equal. Is Java blind, or are we asking the wrong question?

Comparisons make booleans

<, >, <=, >=, == (equal) and != (not equal) compare values. Every comparison produces a boolean: true or false, never 1 or 0.

5 < 7    // true
5 >= 6   // false
5 == 5   // true
5 != 7   // true
🔮 Predict it

Your turn

What does this print?

int a = 3, b = 3;
System.out.println(a <= b);
System.out.println(a != b);
  1. true false
  2. 1 0
  3. false false
Show the answer

3 <= 3 is true, and 3 != 3 is false. Comparisons print as booleans, not numbers.

Primitives: compare values

For primitives, == compares values, after promoting both sides to a common type. So 10 == 10.0 is true (10 becomes 10.0), and 'a' == 97 is true ('a' becomes 97).

Objects: the same object?

For objects, == asks "are these the very same object?" Two separate String objects with the same text are not ==. To compare content, use a.equals(b).

String a = "cat";
String b = "c";
b = b + "at";   // new object
a == b          // false: 2 objects
a.equals(b)     // true: same text
🔮 Predict it

Your turn

What does this print?

String s1 = "dog";
String s2 = "do";
s2 = s2 + "g";
System.out.println(s1 == s2);
System.out.println(s1.equals(s2));
  1. false true
  2. true true
  3. true false
Show the answer

s2 + "g" is built at runtime as a new String object. Same text, different objects: == is false, equals is true.

⚠️ The trap

No chained comparisons

5 < 7 becomes true, and then true < 9 makes no sense: a boolean can't be compared with an int. Write 5 < 7 && 7 < 9.

System.out.println(5 < 7 < 9);  // error
System.out.println(5 < 7 && 7 < 9);
💼 In the real world

In real projects

if (input == "yes") is a classic beginner bug. It can even seem to work, then fail for text typed by a user or read from a file. Professionals compare Strings with equals, often as "yes".equals(input) to be null-safe.

Key takeaways

  1. Comparisons always produce a boolean
  2. == on primitives compares values (with promotion)
  3. == on objects compares references
  4. Use a.equals(b) for String content
🤯 Did you know?

Java keeps String literals in a shared "string pool", so "cat" == "cat" is true: both are the same pooled object. That's exactly why == seems to work... until it doesn't.

Practice questions

What does this print?

int a = 5, b = 7;
System.out.println(a < b);
System.out.println(a != b);
  1. true false
  2. true true
  3. false true
  4. 1 1
Check your answer

true true. 5 < 7 is true and 5 differs from 7, so both comparisons are true. Comparisons produce booleans, not 1 or 0.

What does this print?

String a = "cat";
String b = "c";
b = b + "at";
System.out.println(a == b);
System.out.println(a.equals(b));
  1. false true
  2. true true
  3. true false
  4. false false
Check your answer

false true. The concatenation runs at runtime and creates a new String object, so a and b are different objects with the same text.

Next: && can skip half your condition, and that's a superpower that prevents crashes.