Practice Questions — Installing Java and Setting Up Your Environment

public class EnvCheck {
    public static void main(String[] args) {
        System.out.println("=== Environment Check ===");
        System.out.println("Java Version: " + System.getProperty("java.version"));
        System.out.println("Java Home: " + System.getProperty("java.home"));
        System.out.println("OS: " + System.getProperty("os.name"));
        System.out.println("Processors: " + Runtime.getRuntime().availableProcessors());
        System.out.println("Setup Status: READY");
    }
}

public class WelcomeMessage {
    public static void main(String[] args) {
        String name = "Priya";
        System.out.println("Welcome, " + name + "!");
        System.out.println("You are using Java " + System.getProperty("java.version") + ".");
        System.out.println("Recommended IDE: IntelliJ IDEA Community Edition");
        System.out.println("Tip 1: Always compile before running (javac then java)");
        System.out.println("Tip 2: Read compiler error messages carefully - they tell you exactly what is wrong");
    }
}

public class CompileSteps {
    public static void main(String[] args) {
        System.out.println("=== How to Compile and Run Java ===");
        System.out.println("Step 1: Create source file");
        System.out.println("  File: StudentApp.java");
        System.out.println();
        System.out.println("Step 2: Compile");
        System.out.println("  Command: javac StudentApp.java");
        System.out.println("  Output: StudentApp.class");
        System.out.println();
        System.out.println("Step 3: Run");
        System.out.println("  Command: java StudentApp");
        System.out.println("  (Note: no .class extension!)");
    }
}

public class SystemPropertiesExplorer {
    public static void main(String[] args) {
        System.out.println("=== System Properties Explorer ===");
        String format = "%-17s: %s%n";
        System.out.printf(format, "java.version", System.getProperty("java.version"));
        System.out.printf(format, "java.vendor", System.getProperty("java.vendor"));
        System.out.printf(format, "java.home", System.getProperty("java.home"));
        System.out.printf(format, "os.name", System.getProperty("os.name"));
        System.out.printf(format, "os.arch", System.getProperty("os.arch"));
        System.out.printf(format, "os.version", System.getProperty("os.version"));
        System.out.printf(format, "user.name", System.getProperty("user.name"));
        System.out.printf(format, "user.home", System.getProperty("user.home"));
        System.out.printf(format, "user.dir", System.getProperty("user.dir"));
        System.out.printf(format, "file.separator", System.getProperty("file.separator"));
        System.out.printf(format, "path.separator", System.getProperty("path.separator"));
        System.out.printf(format, "line.separator", System.getProperty("line.separator").replace("\n", "\\n").replace("\r", "\\r"));
    }
}

public class JdkComponents {
    public static void main(String[] args) {
        System.out.println("=== JDK Components Breakdown ===");
        System.out.println();
        System.out.println("JDK (Java Development Kit)");
        System.out.println("|-- Development Tools:");
        System.out.println("|   |-- javac    (Java Compiler)");
        System.out.println("|   |-- jdb      (Java Debugger)");
        System.out.println("|   |-- javadoc  (Documentation Generator)");
        System.out.println("|   |-- jar      (Archive Tool)");
        System.out.println("|   |-- jshell   (Interactive REPL)");
        System.out.println("|");
        System.out.println("|-- JRE (Java Runtime Environment)");
        System.out.println("    |-- Standard Libraries:");
        System.out.println("    |   |-- java.lang  (Core classes)");
        System.out.println("    |   |-- java.util  (Collections, Date)");
        System.out.println("    |   |-- java.io    (File I/O)");
        System.out.println("    |   |-- java.net   (Networking)");
        System.out.println("    |");
        System.out.println("    |-- JVM (Java Virtual Machine)");
        System.out.println("        |-- Class Loader");
        System.out.println("        |-- Bytecode Verifier");
        System.out.println("        |-- Interpreter");
        System.out.println("        |-- JIT Compiler");
        System.out.println("        |-- Garbage Collector");
    }
}

public class ErrorDiagnosis {
    public static void main(String[] args) {
        System.out.println("=== Java Setup Error Diagnosis Guide ===");
        System.out.println();
        System.out.println("[Error 1] 'javac' is not recognized");
        System.out.println("  Cause: JDK bin directory is not in system PATH");
        System.out.println("  Fix: Add %JAVA_HOME%\\bin to PATH, then open a new terminal");
        System.out.println("---");
        System.out.println("[Error 2] UnsupportedClassVersionError");
        System.out.println("  Cause: Compiled with newer JDK, running on older JRE");
        System.out.println("  Fix: Update JRE to match JDK version, or use: javac --release 8 File.java");
        System.out.println("---");
        System.out.println("[Error 3] Could not find or load main class");
        System.out.println("  Cause: Class name mismatch, wrong directory, or missing -cp flag");
        System.out.println("  Fix: Verify class name matches, and use: java -cp bin ClassName");
        System.out.println("---");
        System.out.println("[Error 4] class X is public, should be declared in file named X.java");
        System.out.println("  Cause: File name does not match the public class name");
        System.out.println("  Fix: Rename the file to match the public class name exactly");
        System.out.println("---");
        System.out.println("[Error 5] JAVA_HOME points to a JRE, not a JDK");
        System.out.println("  Cause: JAVA_HOME is set to JRE directory instead of JDK");
        System.out.println("  Fix: Update JAVA_HOME to point to JDK root (containing bin/javac)");
    }
}

public class BuildSimulator {
    public static void main(String[] args) {
        System.out.println("=== Build Simulator ===");
        long time = System.currentTimeMillis();
        System.out.println("[" + time + "] Scanning source directory: src/");
        System.out.println("[" + System.currentTimeMillis() + "] Found: Main.java");
        System.out.println("[" + System.currentTimeMillis() + "] Found: Student.java");
        System.out.println("[" + System.currentTimeMillis() + "] Found: Grade.java");
        System.out.println("[" + System.currentTimeMillis() + "] Compiling 3 source files...");
        System.out.println("[" + System.currentTimeMillis() + "] Generated: bin/Main.class");
        System.out.println("[" + System.currentTimeMillis() + "] Generated: bin/Student.class");
        System.out.println("[" + System.currentTimeMillis() + "] Generated: bin/Grade.class");
        System.out.println("[" + System.currentTimeMillis() + "] Build successful! 3 files compiled.");
        System.out.println("[" + System.currentTimeMillis() + "] Running: java -cp bin Main");
        System.out.println("[" + System.currentTimeMillis() + "] === Application Output ===");
        System.out.println("[" + System.currentTimeMillis() + "] Student Management System v1.0");
        long elapsed = System.currentTimeMillis() - time;
        System.out.println("[" + System.currentTimeMillis() + "] Total build time: " + elapsed + "ms");
    }
}