不同类型的Java类变量初始化方法

Map类型

使用static块

public class LogbackLoggingSystem extends Slf4JLoggingSystem {

  private static final String CONFIGURATION_FILE_PROPERTY = "logback.configurationFile";

  private static final LogLevels<Level> LEVELS = new LogLevels<>();

  static {
    LEVELS.map(LogLevel.TRACE, Level.TRACE);
    LEVELS.map(LogLevel.TRACE, Level.ALL);
    LEVELS.map(LogLevel.DEBUG, Level.DEBUG);
    LEVELS.map(LogLevel.INFO, Level.INFO);
    LEVELS.map(LogLevel.WARN, Level.WARN);
    LEVELS.map(LogLevel.ERROR, Level.ERROR);
    LEVELS.map(LogLevel.FATAL, Level.ERROR);
    LEVELS.map(LogLevel.OFF, Level.OFF);
  }

数组

private static final Class<?>[] EVENT_TYPES = { ApplicationStartingEvent.class,
      ApplicationEnvironmentPreparedEvent.class, ApplicationPreparedEvent.class,
      ContextClosedEvent.class, ApplicationFailedEvent.class };

List类型

也是用static块

public class ApplicationPidFileWriter
    implements ApplicationListener<SpringApplicationEvent>, Ordered {

  private static final Log logger = LogFactory.getLog(ApplicationPidFileWriter.class);

  private static final String DEFAULT_FILE_NAME = "application.pid";

  private static final List<Property> FILE_PROPERTIES;

  static {
    List<Property> properties = new ArrayList<>();
    properties.add(new SpringProperty("spring.pid.", "file"));
    properties.add(new SpringProperty("spring.", "pidfile"));
    properties.add(new SystemProperty("PIDFILE"));
    FILE_PROPERTIES = Collections.unmodifiableList(properties);
  }

  private static final List<Property> FAIL_ON_WRITE_ERROR_PROPERTIES;

  static {
    List<Property> properties = new ArrayList<>();
    properties.add(new SpringProperty("spring.pid.", "fail-on-write-error"));
    properties.add(new SystemProperty("PID_FAIL_ON_WRITE_ERROR"));
    FAIL_ON_WRITE_ERROR_PROPERTIES = Collections.unmodifiableList(properties);
  }