1Z0-811 Practice Test 30 — 15 Questions

Question 1

A developer writes a short program in a file named Hello.java that declares a class named Hello with a main method and prints a greeting. The developer compiles it successfully and then runs the command 'java Hello.java' from the directory containing the source file. Which statement best describes what happens?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

The Java launcher compiles the source file in memory and runs the first top-level class's main method without producing a separate class file.. Running 'java' with a .java file activates the single-file source-code launcher. The compiler processes the source in memory and immediately executes the first top-level class's main method, so no .class file is produced. This differs from the traditional flow of compiling with javac and then launching the resulting class by name.

Answer

The command compiles Hello.java with javac and always writes Hello.class next to the source file before running it.

Answer

The command runs the program only if the class is declared public and the file name exactly matches the public class name, otherwise it aborts.

Answer

The command fails because the launcher requires a compiled class file whose name matches the class, and Hello.class does not exist yet.

Question 2

A developer writes the following method to search a sorted int array for a target value:

```java
public static int search(int[] arr, int target) {
    int lo = 0, hi = arr.length - 1;
    while (lo <= hi) {
        int mid = (lo + hi) / 2;
        if (arr[mid] == target) {
            return mid;
        } else if (arr[mid] < target) {
            lo = mid;
        } else {
            hi = mid;
        }
    }
    return -1;
}
```

When the method is called with a target that exists in the array, the method sometimes never returns. Which change fixes the defect?

Accepted Answer

Change `lo = mid;` to `lo = mid + 1;` and `hi = mid;` to `hi = mid - 1;`. Binary search requires that each iteration strictly reduces the candidate range. Assigning lo or hi to mid without a plus or minus one leaves mid inside the window, so when the window has two elements the same pair can be examined repeatedly and the loop never exits. Moving the bounds one step past mid excludes the already-tested element and guarantees termination.

Answer

Change the loop condition from `lo <= hi` to `lo < hi`

Answer

Change the return type from int to boolean and return false instead of -1

Answer

Change `int mid = (lo + hi) / 2;` to `int mid = (lo + hi + 1) / 2;`

Question 3

A junior developer is learning about Java and asks how Java achieves platform independence. The developer has heard that Java programs run on many different operating systems without recompilation. Which statement best explains how Java provides this capability?

Accepted Answer

Java source code is compiled into bytecode, which is executed by a Java Virtual Machine (JVM) installed on each platform.. Java achieves platform independence by compiling source code into bytecode, a platform-neutral intermediate format. A JVM on each target platform executes that bytecode, translating it to the underlying machine instructions as needed. Because the bytecode does not change across platforms, the same compiled program can run on any system with a compatible JVM, without recompiling from source.

Answer

Java programs are interpreted line by line from the original source file by the Java Runtime Environment without a compilation step.

Answer

Java source code is compiled directly into native machine code for each operating system by the javac tool.

Answer

Java programs use a universal binary format that all operating systems can execute natively without any additional runtime.

Question 4

A developer writes a Java source file named Greeting.java that contains a class named Greeting with a main method. The developer compiles it successfully with javac Greeting.java. Which artifact is produced, and what does it contain?

Accepted Answer

A file named Greeting.class containing Java bytecode that the JVM can execute.. Compiling a Java source file with javac produces a .class file named after the class it contains. That file holds bytecode, a portable intermediate representation executed by the JVM. It is not a native executable, not a JAR archive, and not a modified source file. This bytecode is the key to Java's write-once, run-anywhere capability.

Answer

A file named Greeting.java containing optimized source code for the JVM.

Answer

A file named Greeting.jar containing the compiled class and its dependencies.

Answer

A file named Greeting.exe containing native machine code for the host operating system.

Question 5

A junior developer is writing a Java class to model a bank account. The class needs a field that stores the current balance as a decimal value with high precision, and the field should be accessible only within that same class. Which declaration best meets these requirements?

Accepted Answer

private BigDecimal balance;. Storing monetary values demands a type that preserves decimal precision, and BigDecimal is designed exactly for that purpose, avoiding the rounding artifacts of double and float. Restricting the field with private enforces encapsulation so only the declaring class can touch it directly. The other combinations either lose precision, widen visibility beyond the class, or both, so they do not satisfy the scenario.

Answer

public float balance;

Answer

private double balance;

Answer

protected long balance;

Question 6

A junior developer is reviewing the characteristics of the Java programming language and the Java platform. Which TWO statements accurately describe Java? (Choose two.)

Accepted Answer

The Java Virtual Machine is responsible for executing bytecode and managing memory automatically.. Java source is compiled to bytecode that the JVM executes, and the JVM handles both execution and automatic memory management through garbage collection. Java does not require per-OS recompilation, does not support multiple class inheritance, and does not require manual deallocation. These two properties, portable bytecode and JVM-managed memory, are fundamental to the platform.

Answer

Java programs must be recompiled separately for each operating system before they can run.

Answer

Java requires developers to manually deallocate objects using a free method.

Answer

Java supports multiple inheritance of classes to promote code reuse.

Question 7

A developer is writing a utility that must print each character of a String on its own line. The code is:

```java
String word = "Java";
for (int i = 0; i <= word.length(); i++) {
    System.out.println(word.charAt(i));
}
```

When run, the program prints the four characters correctly but then throws an exception. What is the cause and the correct fix?

Accepted Answer

The condition should be `i < word.length()`, because valid indices run from 0 to length() - 1 and index length() is out of range. The loop condition i <= word.length() allows one iteration too many. Because charAt accepts indices from 0 through length() - 1, the final pass attempts to read a nonexistent position and throws StringIndexOutOfBoundsException. Replacing the inclusive comparison with a strict less-than comparison keeps every access inside the valid range.

Answer

The condition should be `i <= word.length() - 1` and the loop variable must be declared outside the for statement

Answer

The call to println should be changed to print, because println cannot accept a char argument

Answer

The loop variable should start at 1 instead of 0, because charAt is one-based

Question 8

A developer new to Java writes a source file that begins with the line 'public class HelloWorld {' and saves it as hello.java. When compiling with javac hello.java, the compiler reports an error. What is the most likely cause?

Accepted Answer

The file name must match the public class name, so it should be HelloWorld.java.. Java requires that a source file containing a public class be named exactly after that class, matching case. The declared public class is HelloWorld, so the file must be HelloWorld.java. The name hello.java does not match, causing javac to fail. A main method, private modifier, or .class extension would not fix this naming rule violation.

Answer

The file extension should be .class instead of .java for compilation.

Answer

The main method is missing from the class, so javac cannot compile it.

Answer

The class must be declared as private instead of public to compile.

Question 9

A company is deploying a Java application that must run on a variety of devices, including some with limited memory and processing power. The application does not require a graphical user interface and will be used for simple data collection. Which Java edition is specifically designed for such constrained environments?

Accepted Answer

Java ME. Java ME is the edition designed for embedded and mobile devices with constrained resources. It offers a subset of Java SE APIs and configurations tailored to limited memory and processing power. Java SE and Java EE target more capable systems, while Java Card is for smart cards. The scenario's requirements match Java ME's purpose.

Answer

Java Card

Answer

Java EE

Answer

Java SE

Question 10

A developer is writing a method that should double every element in an int array passed as an argument. The method signature is public static void doubleAll(int[] nums). The developer wants the caller's original array to reflect the doubled values. Which implementation correctly achieves this?

Accepted Answer

for (int i = 0; i < nums.length; i++) { nums[i] *= 2; }. Arrays are objects, and Java passes object references by value. When a method receives an array reference, it can modify the array's elements, and those changes are visible to the caller. Reassigning the parameter to a new array does not affect the caller's reference. The correct implementation iterates from 0 to nums.length - 1 and updates each element in place using compound assignment.

Answer

nums = new int[nums.length]; for (int i = 0; i < nums.length; i++) { nums[i] *= 2; }

Answer

int[] doubled = new int[nums.length]; for (int i = 0; i < nums.length; i++) { doubled[i] = nums[i] * 2; } nums = doubled;

Answer

for (int i = 0; i <= nums.length; i++) { nums[i] *= 2; }

Question 11

A junior developer writes a Java source file named Payroll.java in a project folder. They open a terminal in that folder and run the command: javac Payroll.java. The command completes with no messages, and a new file named Payroll.class appears in the folder. What has actually happened?

Accepted Answer

The Java compiler translated the source code into platform-independent bytecode.. The javac tool compiles Java source into bytecode stored in .class files. Bytecode is a portable intermediate representation that is not tied to any processor or operating system, which is the foundation of Java's platform independence. Since javac only compiles, no program logic runs, so a silent, successful command with a new class file is the expected, normal outcome.

Answer

The file was only syntax-checked, and no output artifact is created by javac.

Answer

The JVM executed the class and produced the .class file as a log of the run.

Answer

The source file was converted into native machine code for the local processor.

Question 12

A team is documenting the execution model of their Java service for new hires. They want to describe accurately what happens between launching the application and the code running on the server's processor. Which two statements correctly describe this execution model? (Choose two.)

Accepted Answer

The JVM loads class files, verifies the bytecode, and interprets or just-in-time compiles it for the host machine.. Java execution relies on loading and verifying portable bytecode, then interpreting or just-in-time compiling it for the host processor, with a garbage collector reclaiming unreachable objects automatically. Bytecode stays platform-neutral, so no recompilation per server is needed, and compilation is selective rather than exhaustive, targeting only methods that prove hot during execution.

Answer

Class files must be recompiled with javac on each target server before the application can start there.

Answer

Bytecode produced by javac is bound to the operating system and processor of the machine where it was compiled.

Answer

Every method is compiled to native machine code before the program's main method begins executing.

Question 13

A developer is writing a method that must accept and manipulate whole-number values that can be negative, and also needs a type suitable for storing a single Unicode character. Which two primitive types are appropriate for these requirements? (Choose two.)

Accepted Answer

char. The requirements call for a primitive that stores signed whole numbers and a primitive that stores a single character. int handles negative and positive whole numbers, and char handles one Unicode character. boolean stores only truth values, float is for decimal numbers and is not exact, and String is a reference type for character sequences, so none of those meet the stated needs.

Answer

String

Answer

boolean

Answer

float

Question 14

A developer is reviewing a Java program that uses a class named String from the java.lang package. The developer notices that no import statement for java.lang is present in the source file, yet the program compiles successfully. The developer asks why the import is not required. Which statement best explains this behavior?

Accepted Answer

The java.lang package is automatically imported by the compiler into every Java source file.. Java automatically imports all classes in the java.lang package into every source file. This built-in import allows commonly used types such as String, System, and Object to be referenced without explicit import statements. In the scenario, the String class is in java.lang, so no import is needed. Other packages do not receive this automatic treatment and require explicit imports or fully qualified names.

Answer

The compiler resolves any class name by searching all packages on the classpath without requiring imports.

Answer

The String class is a primitive type built into the Java language, so it does not require an import.

Answer

The java.lang package is imported automatically only when the source file contains a package declaration.

Question 15

A team is evaluating Java for a new cross-platform project. The team lead asks for a summary of key characteristics of the Java programming language and platform. Which two statements accurately describe Java? (Choose two.)

Accepted Answer

Java provides automatic memory management through garbage collection.. Java is an object-oriented language that supports encapsulation, inheritance, and polymorphism, and it provides automatic memory management through garbage collection. These are core characteristics of the language and platform. Java does not support direct pointer manipulation, and its source code is compiled to portable bytecode rather than native machine code, so it does not need to be recompiled for each operating system.

Answer

Java programs are compiled to native machine code for the target platform before execution.

Answer

Java source code must be recompiled separately for each operating system before it can run.

Answer

Java allows direct manipulation of memory addresses using pointers.