[Java知识库]关于super与this你知多少1

一、super调用父类的构造方法

1、MyBatis的BaseBuilder

/**
 * @author Clinton Begin
 */
public abstract class BaseBuilder {
  protected final Configuration configuration;
  protected final TypeAliasRegistry typeAliasRegistry;
  protected final TypeHandlerRegistry typeHandlerRegistry;

  public BaseBuilder(Configuration configuration) {
    this.configuration = configuration;
    this.typeAliasRegistry = this.configuration.getTypeAliasRegistry();
    this.typeHandlerRegistry = this.configuration.getTypeHandlerRegistry();
  }
}

2、MyBatis的SqlSourceBuilder，也就是BaseBuilder的子类

? ? ?super调用父类的构造方法初始化configuration，实质上configuration也是SqlSourceBuilder的成员变量，不过继承了父类的就不必重复写了，super调用父类构造方法也就是对自己的configuration成员变量初始化了。初始化后就可以在parse()方法里面引用configuration了。如果不初始化，parse()方法里面configuration调用isShrinkWhitespacesInSql()方法就报NULL异常！

/**
 * @author Clinton Begin
 */
public class SqlSourceBuilder extends BaseBuilder {

  private static final String PARAMETER_PROPERTIES = "javaType,jdbcType,mode," +
    "numericScale,resultMap,typeHandler,jdbcTypeName";

  public SqlSourceBuilder(Configuration configuration) {
    // 调用父类的构造方法初始化configuration，实质上configuration也是SqlSourceBuilder的成员变量，
    // 不过继承了父类的就不必重复写了，super调用父类构造方法也就是对自己的configuration成员变量初始化了
    super(configuration);
  }

  public SqlSource parse(String originalSql,
                         Class<?> parameterType,
                         Map<String, Object> additionalParameters) {
    ParameterMappingTokenHandler handler = new ParameterMappingTokenHandler(configuration
      , parameterType, additionalParameters);
    GenericTokenParser parser = new GenericTokenParser("#{"
      , "}", handler);
    String sql;
    if (configuration.isShrinkWhitespacesInSql()) {
      sql = parser.parse(removeExtraWhitespaces(originalSql));
    } else {
      sql = parser.parse(originalSql);
    }
    return new StaticSqlSource(configuration, sql, handler.getParameterMappings());
  }
}