Java OCP Practice Questions: Building Blocks, with Answers Explained

The OCP Java exam doesn’t test whether you can write code. It tests whether you can read code like a compiler: which line fails, what exactly gets printed, which object is gone. Try these ten questions before you open the answers.

They cover the “Java building blocks” topics of the Oracle Certified Professional exam for Java SE 17 (1Z0-829). The same rules also apply to the Java SE 21 exam (1Z0-830). Every answer below was checked by compiling and running the code with Java 17 rules.

1. Default Values

What does this program print?

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public class Defaults {
    static boolean flag;
    static char letter;
    static double ratio;
    static String name;
    static int[] scores = new int[2];

    public static void main(String[] args) {
        System.out.println(flag + " " + ratio + " " + name + " " + scores[1]);
        System.out.println((int) letter);
    }
}

• A. false 0.0 null 0, then 0
• B. false 0 null 0, then an empty line
• C. false 0.0 0, then 0
• D. The code does not compile, because name is never initialized.
• E. A NullPointerException is thrown.

2. Definite Assignment

Does this method compile?

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public class Shipping {
    static int cost(boolean express, int weight) {
        int base;
        if (weight > 10) {
            base = 20;
        } else if (weight > 0) {
            base = 10;
        }
        int extra;
        if (express) extra = 5; else extra = 0;
        return base + extra;
    }
}

• A. Yes.
• B. No, because base might not be initialized.
• C. No, because extra might not be initialized.
• D. No, because of both base and extra.

Practice explaining answers like these out loud: that’s what technical interviews test. Real Java Coding Interview Questions covers the Java questions interviewers ask most.

3. Local Variable Type Inference with var

Which of these lines compile as local variable declarations inside a method? (Choose all that apply.)

• A. var count = 10, total = 20;
• B. var price = 9.99f;
• C. var empty = null;
• D. var var = "var";
• E. var numbers = {1, 2, 3};
• F. var names = new ArrayList<>();
• G. var counter;

4. Numeric Literals

Which declarations compile? (Choose all that apply.)

• A. int million = 1_000_000;
• B. int hex = 0x_FF;
• C. double pi = 3._14;
• D. long big = 3_000_000_000;
• E. long big2 = 3_000_000_000L;
• F. int bits = 0b1010__1010;
• G. int trailing = 100_;

5. Variable Scope

How many variables are in scope at the line marked // HERE?

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public class Inventory {
    static int warehouses = 3;
    String region;

    void audit(int[] stock) {
        int total = 0;
        for (int i = 0; i < stock.length; i++) {
            int item = stock[i];
            total += item;
        }
        if (total > 100) {
            boolean large = true;
        }
        String label = "audit";
        // HERE
    }
}

• A. 3
• B. 4
• C. 5
• D. 6
• E. 7
• F. 8

Want to go deeper than practice questions? This is the study guide most OCP candidates use, with every exam objective explained: OCP Oracle Certified Professional Java SE 17 Developer Study Guide.

6. Text Blocks

Which statements about the output are true? (Choose all that apply.)

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public class Query {
    public static void main(String[] args) {
        String sql = """
            SELECT id, name
              FROM users \
            WHERE active = true
            """;
        System.out.print(sql);
    }
}

• A. The output has two lines.
• B. The output has three lines.
• C. The second line starts with two spaces.
• D. Every line starts with four spaces.
• E. The printed text ends with a line break.
• F. The code does not compile.

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SELECT id, name
  FROM users WHERE active = true

7. Garbage Collection

Which statement is true?

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public class Session {
    Session next;

    public static void main(String[] args) {
        Session s1 = new Session();   // object A
        Session s2 = new Session();   // object B
        Session s3 = new Session();   // object C
        s1.next = s2;
        s2.next = s3;
        s2 = null;                    // point 1
        s3 = s1;                      // point 2
        s1 = null;                    // point 3
        s3.next = null;               // point 4
    }
}

• A. Object B is eligible for garbage collection after point 1.
• B. Object C is eligible for garbage collection after point 2.
• C. Object A is eligible for garbage collection after point 3.
• D. Objects B and C are eligible for garbage collection after point 4.
• E. Object A is eligible for garbage collection after point 4.
• F. Calling System.gc() after point 4 guarantees that B and C are removed.

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start    s1 -> A -> B -> C      s2 -> B      s3 -> C
point 1  s1 -> A -> B -> C                   s3 -> C
point 2  s1 -> A -> B -> C      s3 -> A      (C still reachable through A -> B -> C)
point 3                         s3 -> A -> B -> C
point 4                         s3 -> A      (A.next is null: B and C are unreachable)

8. Primitive Conversions

Given byte level = 10;, which statements compile? (Choose all that apply.)

• A. level = level + 1;
• B. level += 1;
• C. float rate = 2.5;
• D. char c = 'a' + 1;
• E. short s = 40_000;
• F. long total = level * 2;
• G. int x = 7 / 2.0;

9. Autoboxing and Equality

With default JVM settings, what does this print?

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public class Boxes {
    public static void main(String[] args) {
        Integer a = 127, b = 127;
        Integer c = 128, d = 128;
        Long e = 127L;
        System.out.println(a == b);
        System.out.println(c == d);
        System.out.println(c.equals(d));
        System.out.println(a.equals(e));
        System.out.println(a == 127);
    }
}

• A. true true true true true
• B. true false true false true
• C. true false true true true
• D. false false true false true
• E. The code does not compile.

(Each value is printed on its own line.)

10. Imports

This class does not compile. Which changes make it compile? (Choose all that apply.)

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import java.util.*;
import java.sql.*;

public class Report {
    Date created;
}

• A. Remove import java.sql.*;
• B. Add import java.util.Date;
• C. Add import java.lang.*;
• D. Change the field to java.util.Date created;
• E. Add both import java.util.Date; and import java.sql.Date;
• F. No change is needed: the code compiles.

How Did You Do?

• 9–10 correct: you read code like a compiler. You’re ready for this part of the exam.
• 6–8 correct: solid. Review the topics you missed; they are the classic traps.
• 0–5 correct: go through the explanations again. These rules come back in every chapter of the exam.

Certification questions and interview questions test the same skill: reading code carefully and explaining your reasoning.

Interviews go one step further and ask you to write the code yourself. Practice with real interview questions, solved step by step:

Real-world examples, diagrams, and explanations that make complex systems simple.