assertSame and assertNotSame in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of assertSame with identical objects

What will be the result of this JUnit test method execution?

JUnit

String a = "test";
String b = a;
assertSame(a, b);

A Test throws NullPointerException

B Test fails with AssertionError

C Test passes without error

D Compilation error due to assertSame usage

💡 Hint

assertSame checks if both references point to the exact same object.

Since both variables 'a' and 'b' refer to the same String object, assertSame passes.

❓ Predict Output

intermediate

Result of assertNotSame with different objects

What happens when this JUnit assertion runs?

JUnit

String a = new String("hello");
String b = new String("hello");
assertNotSame(a, b);

A Test passes without error

B Test fails with AssertionError

C Compilation error due to assertNotSame usage

D Test throws IllegalArgumentException

💡 Hint

assertNotSame checks that two references do not point to the same object.

Though the strings have the same content, 'a' and 'b' are different objects, so assertNotSame passes.

❓ assertion

advanced

Which assertion fails here?

Given these variables, which assertion will fail when executed?

JUnit

Integer x = 128;
Integer y = 128;
assertSame(x, y);
assertNotSame(x, y);

A Both assertions pass

B assertNotSame(x, y) fails

C Both assertions fail

D assertSame(x, y) fails

💡 Hint

Integer caching affects small values but not 128.

For Integer 128, 'x' and 'y' are different objects, so assertSame fails but assertNotSame passes.

🧠 Conceptual

advanced

Purpose of assertSame vs assertEquals

Which statement correctly explains the difference between assertSame and assertEquals in JUnit?

A assertSame checks if two references point to the same object; assertEquals checks if two objects are logically equal.

B assertSame checks object content equality; assertEquals checks reference equality.

C assertSame throws exception on nulls; assertEquals ignores nulls.

D assertSame compares primitive values; assertEquals compares object references.

💡 Hint

Think about identity vs equality.

assertSame tests if two variables refer to the exact same object instance; assertEquals tests if two objects are equal in value.

🔧 Debug

expert

Why does this assertSame fail unexpectedly?

Consider this test code snippet: String a = "abc"; String s1 = a + "def"; String s2 = "abcdef"; assertSame(s1, s2); Why does assertSame fail here?

A Because assertSame cannot be used with String objects

B Because string concatenation at runtime creates new objects, so references differ

C Because s1 and s2 are different String objects despite having same content

D Because s2 is null causing NullPointerException

💡 Hint

Consider when Java creates String objects and how concatenation works.

The expression a + "def" is evaluated at runtime creating a new String object, so s1 and s2 reference different objects.