feat(environment): Add more Javadoc

Author: PerfectSlayer

components/environment/src/main/java/datadog/environment/CommandLine.java

@@ -6,31 +6,40 @@
 import java.util.Arrays;
 import java.util.List;
 
-/** Fetches and captures the command line, both command and its arguments. */
+/**
+ * Fetches and captures the command line, both command and its arguments. It relies on a
+ * non-standard {@code sun.java.command} system property and was tested on:
+ *
+ * <ul>
+ *   <li>OracleJDK,
+ *   <li>OpenJDK,
+ *   <li>Temurin based JDK,
+ *   <li>IMB JDK,
+ *   <li>Azul Zulu,
+ *   <li>Amazon Coretto,
+ * </ul>
+ */
 class CommandLine {
-  final List<String> FULL_CMD = findFullCommand();
-  final String CMD = getCommand();
-  final List<String> CMD_ARGUMENTS = getCommandArguments();
+  private static final String SUN_JAVA_COMMAND_PROPERTY = "sun.java.command";
+  final List<String> fullCommand = findFullCommand();
+  final String command = getCommand();
+  final List<String> arguments = getCommandArguments();
 
   @SuppressForbidden // split on single-character uses fast path
   private List<String> findFullCommand() {
-    // Besides "sun.java.command" property is not an standard, all main JDKs has set this
-    // property.
-    // Tested on:
-    // - OracleJDK, OpenJDK, AdoptOpenJDK, IBM JDK, Azul Zulu JDK, Amazon Coretto JDK
-    String command = SystemProperties.getOrDefault("sun.java.command", "").trim();
+    String command = SystemProperties.getOrDefault(SUN_JAVA_COMMAND_PROPERTY, "").trim();
     return command.isEmpty() ? emptyList() : Arrays.asList(command.split(" "));
   }
 
   private String getCommand() {
-    return FULL_CMD.isEmpty() ? null : FULL_CMD.get(0);
+    return fullCommand.isEmpty() ? null : fullCommand.get(0);
   }
 
   private List<String> getCommandArguments() {
-    if (FULL_CMD.isEmpty()) {
-      return FULL_CMD;
+    if (fullCommand.isEmpty()) {
+      return fullCommand;
     } else {
-      return FULL_CMD.subList(1, FULL_CMD.size());
+      return fullCommand.subList(1, fullCommand.size());
     }
   }
 }

components/environment/src/main/java/datadog/environment/EnvironmentVariables.java

@@ -3,7 +3,12 @@
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
-/** Safely queries environment variables. */
+/**
+ * Safely queries environment variables against security manager.
+ *
+ * @see <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/SecurityManager.html">Security
+ *     Manager</a>
+ */
 public final class EnvironmentVariables {
   private EnvironmentVariables() {}
 

components/environment/src/main/java/datadog/environment/JavaVirtualMachine.java

@@ -136,7 +136,7 @@ public static List<String> getVmOptions() {
    * @return The command arguments, an empty collection if missing or can't be retrieved.
    */
   public static List<String> getCommandArguments() {
-    return commandLine.CMD_ARGUMENTS;
+    return commandLine.arguments;
   }
 
   /**
@@ -146,7 +146,9 @@ public static List<String> getCommandArguments() {
    *     retrieved.
    */
   public static @Nullable String getMainClass() {
-    return commandLine.CMD != null && !isJarName(commandLine.CMD) ? commandLine.CMD : null;
+    return commandLine.command != null && !isJarName(commandLine.command)
+        ? commandLine.command
+        : null;
   }
 
   /**
@@ -156,7 +158,9 @@ public static List<String> getCommandArguments() {
    *     retrieved.
    */
   public static @Nullable String getJarFile() {
-    return commandLine.CMD != null && isJarName(commandLine.CMD) ? commandLine.CMD : null;
+    return commandLine.command != null && isJarName(commandLine.command)
+        ? commandLine.command
+        : null;
   }
 
   private static boolean isJarName(String argument) {

components/environment/src/main/java/datadog/environment/OperatingSystem.java

@@ -10,6 +10,7 @@
 import java.util.Arrays;
 import java.util.Locale;
 
+/** Detects operating systems and libc library. */
 public final class OperatingSystem {
   private OperatingSystem() {}
 

components/environment/src/main/java/datadog/environment/SystemProperties.java

@@ -1,6 +1,11 @@
 package datadog.environment;
 
-/** Safely queries system properties. */
+/**
+ * Safely queries system properties against security manager.
+ *
+ * @see <a href="https://docs.oracle.com/javase/8/docs/api/java/lang/SecurityManager.html">Security
+ *     Manager</a>
+ */
 public final class SystemProperties {
   private SystemProperties() {}
 
@@ -30,11 +35,18 @@ public static String getOrDefault(String property, String defaultValue) {
     }
   }
 
+  /**
+   * Sets a system property value.
+   *
+   * @param property The system property name.
+   * @param value The system property value to set.
+   * @return {@code true} if the system property was successfully set, {@code} false otherwise.
+   */
   public static boolean set(String property, String value) {
     try {
       System.setProperty(property, value);
       return true;
-    }  catch (SecurityException ignored) {
+    } catch (SecurityException ignored) {
       return false;
     }
   }