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h2/src/main/org/h2/expression/Aggregate.java

@@ -36,9 +36,8 @@ import org.h2.value.ValueNull;
 import org.h2.value.ValueString;
 
 /**
- * @author Thomas
+ * Implements the integrated aggregate functions, such as COUNT, MAX, SUM.
  */
-
 public class Aggregate extends Expression {
     // TODO incompatibility to hsqldb: aggregates: hsqldb uses automatic data
     // type for sum if value is too big,

h2/src/main/org/h2/expression/AggregateData.java

@@ -18,6 +18,9 @@ import org.h2.value.ValueInt;
 import org.h2.value.ValueLong;
 import org.h2.value.ValueNull;
 
+/**
+ * Data stored while calculating an aggregate.
+ */
 public class AggregateData {
     private final int aggregateType;
     private long count;

h2/src/main/org/h2/expression/Alias.java

@@ -12,11 +12,9 @@ import org.h2.table.ColumnResolver;
 import org.h2.table.TableFilter;
 import org.h2.value.Value;
 
-
 /**
- * @author Thomas
+ * A column alias as in SELECT 'Hello' AS NAME ...
  */
-
 public class Alias extends Expression {
 
     private final String alias;

h2/src/main/org/h2/expression/CompareLike.java

@@ -22,9 +22,8 @@ import org.h2.value.ValueNull;
 import org.h2.value.ValueString;
 
 /**
- * @author Thomas
+ * Pattern matching comparison expression: WHERE NAME LIKE ?
  */
-
 public class CompareLike extends Condition {
 
     private final CompareMode compareMode;
@@ -129,7 +128,7 @@ public class CompareLike extends Condition {
         // (at prepare time)
         // otherwise we would need to prepare at execute time,
         // which is maybe slower (but maybe not in this case!)
-        // TODO optimizer: like: check what other databases do!
+        // TODO optimizer: like: check what other databases do
         if (!right.isValueSet()) {
             return;
         }

h2/src/main/org/h2/expression/Condition.java

@@ -8,7 +8,7 @@ import org.h2.value.Value;
 import org.h2.value.ValueBoolean;
 
 /**
- * @author Thomas
+ * Represents a condition returning a boolean value, or NULL.
  */
 public abstract class Condition extends Expression {
 

h2/src/main/org/h2/expression/ConditionAndOr.java

@@ -17,7 +17,7 @@ import org.h2.value.ValueBoolean;
 import org.h2.value.ValueNull;
 
 /**
- * @author Thomas
+ * An 'and' or 'or' condition as in WHERE ID=1 AND NAME=?
  */
 public class ConditionAndOr extends Condition {
 

h2/src/main/org/h2/expression/ConditionExists.java

@@ -15,9 +15,8 @@ import org.h2.value.Value;
 import org.h2.value.ValueBoolean;
 
 /**
- * @author Thomas
+ * An 'exists' condition as in WHERE EXISTS(SELECT ...)
  */
-
 public class ConditionExists extends Condition {
 
     private final Query query;

h2/src/main/org/h2/expression/ConditionIn.java

@@ -24,9 +24,8 @@ import org.h2.value.ValueBoolean;
 import org.h2.value.ValueNull;
 
 /**
- * @author Thomas
+ * An 'in' condition with a list of values, as in WHERE NAME IN(...)
  */
-
 public class ConditionIn extends Condition {
 
     private final Database database;

h2/src/main/org/h2/expression/ConditionInSelect.java

@@ -21,7 +21,7 @@ import org.h2.value.ValueBoolean;
 import org.h2.value.ValueNull;
 
 /**
- * @author Thomas
+ * An 'in' condition with a subquery, as in WHERE ID IN(SELECT ...)
  */
 public class ConditionInSelect extends Condition {
     private Database database;

h2/src/main/org/h2/expression/ConditionNot.java

@@ -13,6 +13,9 @@ import org.h2.table.TableFilter;
 import org.h2.value.Value;
 import org.h2.value.ValueNull;
 
+/**
+ * A NOT condition.
+ */
 public class ConditionNot extends Condition {
 
     private Expression condition;

h2/src/main/org/h2/expression/Expression.java

@@ -14,7 +14,6 @@ import org.h2.table.TableFilter;
 import org.h2.util.StringUtils;
 import org.h2.value.Value;
 
-
 /**
  * An expression is a operation, a value, or a function in a query.
  */
@@ -22,82 +21,257 @@ public abstract class Expression {
 
     private boolean addedToFilter;
 
+    /**
+     * Return the resulting value for the current row.
+     *
+     * @param session the session
+     * @return the result
+     */
     public abstract Value getValue(Session session) throws SQLException;
+
+    /**
+     * Return the data type. The data type may not be known before the optimization phase.
+     *
+     * @param session the session
+     * @return the type
+     */
     public abstract int getType();
+
+    /**
+     * Map the columns of the resolver to expression columns.
+     *
+     * @param resolver the column resolver
+     * @return level the subquery nesting level
+     */
     public abstract void mapColumns(ColumnResolver resolver, int level) throws SQLException;
+
+    /**
+     * Try to optimize the expression.
+     *
+     * @param session the session
+     * @return the optimized expression
+     */
     public abstract Expression optimize(Session session) throws SQLException;
-    public abstract void setEvaluatable(TableFilter tableFilter, boolean b);
+
+    /**
+     * Tell the expression columns whether the table filter can return values now.
+     * This is used when optimizing the query.
+     *
+     * @param tableFilter the table filter
+     * @param value true if the table filter can return value
+     */
+    public abstract void setEvaluatable(TableFilter tableFilter, boolean value);
+
+    /**
+     * Get the scale of this expression.
+     *
+     * @return the scale
+     */
     public abstract int getScale();
+
+    /**
+     * Get the precision of this expression.
+     *
+     * @return the precision
+     */
     public abstract long getPrecision();
+
+    /**
+     * Get the display size of this expression.
+     *
+     * @return the display size
+     */
     public abstract int getDisplaySize();
+
+    /**
+     * Get the SQL statement of this expression.
+     * This may not always be the original SQL statement,
+     * specially after optimization.
+     *
+     * @return the SQL statement
+     */
     public abstract String getSQL();
+
+    /**
+     * Update an aggregate value.
+     * This method is called at statement execution time once for each row.
+     *
+     * @param session the session
+     */
     public abstract void updateAggregate(Session session) throws SQLException;
+
+    /**
+     * Check if this expression and all sub-expressions can fulfill a criteria.
+     * If any part returns false, the result is false.
+     *
+     * @param visitor the visitor
+     * @return if the criteria can be fulfilled
+     */
     public abstract boolean isEverything(ExpressionVisitor visitor);
+
+    /**
+     * Estimate the cost to process the expression.
+     * Used when optimizing the query, to calculate the query plan
+     * with the lowest estimated cost.
+     *
+     * @return the estimated cost
+     */
     public abstract int getCost();
 
+    /**
+     * Check if this expression and all sub-expressions can fulfill a criteria.
+     * This is a convenience function.
+     *
+     * @param expressionVisitorType the visitor type
+     * @return if the criteria can be fulfilled
+     */
     public final boolean isEverything(int expressionVisitorType) {
         ExpressionVisitor visitor = ExpressionVisitor.get(expressionVisitorType);
         return isEverything(visitor);
     }
 
+    /**
+     * If it is possible, return the negated expression. This is used
+     * to optimize NOT expressions: NOT ID>10 can be converted to
+     * ID<=10. Returns null if negating is not possible.
+     *
+     * @param session the session
+     * @return the negated expression, or null
+     */
     public Expression getNotIfPossible(Session session) {
         // by default it is not possible
         return null;
     }
 
+    /**
+     * Check if this expression will always return the same value.
+     *
+     * @return if the expression is constant
+     */
     public boolean isConstant() {
         return false;
     }
 
+    /**
+     * Is the value of a parameter set.
+     *
+     * @return if it is set
+     */
     public boolean isValueSet() {
         return false;
     }
 
+    /**
+     * Check if this is an auto-increment column.
+     *
+     * @return true if it is an auto-increment column
+     */
     public boolean isAutoIncrement() {
         return false;
     }
 
+    /**
+     * Get the value in form of a boolean expression.
+     * Returns true, false, or null.
+     * In this database, everything can be a condition.
+     *
+     * @param session the session
+     * @return the result
+     */
     public Boolean getBooleanValue(Session session) throws SQLException {
-        // TODO optimization: is this required?
         return getValue(session).getBoolean();
     }
 
+    /**
+     * Create index conditions if possible and attach them to the table filter.
+     *
+     * @param session the session
+     * @param filter the table filter
+     */
     public void createIndexConditions(Session session, TableFilter filter) throws SQLException {
         // default is do nothing
     }
 
+    /**
+     * Get the column name or alias name of this expression.
+     *
+     * @return the column name
+     */
     public String getColumnName() {
         return getAlias();
     }
 
+    /**
+     * Get the schema name, or null
+     *
+     * @return the schema name
+     */
     public String getSchemaName() {
         return null;
     }
 
+    /**
+     * Get the table name, or null
+     *
+     * @return the table name
+     */
     public String getTableName() {
         return null;
     }
 
+    /**
+     * Check whether this expression is a column and can store null values.
+     *
+     * @return whether null values are allowed
+     */
     public int getNullable() {
         return Column.NULLABLE_UNKNOWN;
     }
 
+    /**
+     * Get the table alias name or null
+     * if this expression does not represent a column.
+     *
+     * @return the table alias name
+     */
     public String getTableAlias() {
         return null;
     }
 
+    /**
+     * Get the alias name of a column or SQL expression
+     * if it is not an aliased expression.
+     *
+     * @return the alias name
+     */
     public String getAlias() {
         return StringUtils.unEnclose(getSQL());
     }
 
+    /**
+     * Only returns true if the expression is a wildcard.
+     *
+     * @return if this expression is a wildcard
+     */
     public boolean isWildcard() {
         return false;
     }
 
+    /**
+     * Returns the main expression, skipping aliases.
+     *
+     * @return the expression
+     */
     public Expression getNonAliasExpression() {
         return this;
     }
 
+    /**
+     * Add conditions to a table filter if they can be evaluated.
+     *
+     * @param filter the table filter
+     * @param outerJoin if the expression is part of an outer join
+     */
     public void addFilterConditions(TableFilter filter, boolean outerJoin) {
         if (!addedToFilter && !outerJoin && isEverything(ExpressionVisitor.EVALUATABLE)) {
             filter.addFilterCondition(this, false);
@@ -105,10 +279,22 @@ public abstract class Expression {
         }
     }
 
+    /**
+     * Convert this expression to a String.
+     *
+     * @return the string representation
+     */
     public String toString() {
         return getSQL();
     }
 
+    /**
+     * Optimize IN(...) expressions if possible.
+     *
+     * @param session the session
+     * @param select the query
+     * @return the optimized expression
+     */
     public Expression optimizeInJoin(Session session, Select select) throws SQLException {
         return this;
     }

h2/src/main/org/h2/expression/ExpressionColumn.java

@@ -23,6 +23,9 @@ import org.h2.table.TableFilter;
 import org.h2.value.Value;
 import org.h2.value.ValueBoolean;
 
+/**
+ * A expression that represents a column of a table or view.
+ */
 public class ExpressionColumn extends Expression {
     private Database database;
     private String schemaName;

h2/src/main/org/h2/expression/ExpressionList.java

@@ -12,6 +12,10 @@ import org.h2.table.TableFilter;
 import org.h2.value.Value;
 import org.h2.value.ValueArray;
 
+/**
+ * A list of expressions, as in (ID, NAME).
+ * The result of this expression is an array.
+ */
 public class ExpressionList extends Expression {
 
     private Expression[] list;

h2/src/main/org/h2/expression/ExpressionVisitor.java

@@ -7,6 +7,10 @@ package org.h2.expression;
 import org.h2.table.ColumnResolver;
 import org.h2.table.Table;
 
+/**
+ * The visitor pattern is used to iterate through all expressions of a query
+ * to optimize a statement.
+ */
 public class ExpressionVisitor {
     // Is the value independent on unset parameters or on columns of a higher level query, or sequence values (that means can it be evaluated right now)
     public static final int INDEPENDENT = 0;

h2/src/main/org/h2/expression/Function.java

@@ -56,9 +56,8 @@ import org.h2.value.ValueTimestamp;
 import org.h2.value.ValueUuid;
 
 /**
- * @author Thomas
+ * This class implements most built-in functions of this database.
  */
-
 public class Function extends Expression implements FunctionCall {
     // TODO functions: add function hashcode(value)
 

h2/src/main/org/h2/expression/FunctionCall.java

@@ -10,6 +10,10 @@ import org.h2.engine.Session;
 import org.h2.value.Value;
 import org.h2.value.ValueResultSet;
 
+/**
+ * This interface is used by the built-in functions,
+ * as well as the user defined functions.
+ */
 public interface FunctionCall {
 
     String getName();

h2/src/main/org/h2/expression/FunctionInfo.java

@@ -4,6 +4,9 @@
  */
 package org.h2.expression;
 
+/**
+ * This class contains information about a built-in function.
+ */
 class FunctionInfo {
     String name;
     int type;

h2/src/main/org/h2/expression/JavaAggregate.java

@@ -21,6 +21,9 @@ import org.h2.value.DataType;
 import org.h2.value.Value;
 import org.h2.value.ValueNull;
 
+/**
+ * This class wrapps a user defined aggregate.
+ */
 public class JavaAggregate extends Expression {
 
     private final UserAggregate userAggregate;

h2/src/main/org/h2/expression/JavaFunction.java

@@ -15,6 +15,9 @@ import org.h2.value.Value;
 import org.h2.value.ValueNull;
 import org.h2.value.ValueResultSet;
 
+/**
+ * This class wrapps a user defined function.
+ */
 public class JavaFunction extends Expression implements FunctionCall {
 
     private FunctionAlias functionAlias;

h2/src/main/org/h2/expression/Operation.java

@@ -16,6 +16,9 @@ import org.h2.value.Value;
 import org.h2.value.ValueNull;
 import org.h2.value.ValueString;
 
+/**
+ * A mathematical expression, or string concatenation.
+ */
 public class Operation extends Expression {
     public static final int CONCAT = 0, PLUS = 1, MINUS = 2, MULTIPLY = 3, DIVIDE = 4, NEGATE = 5;
     private int opType;

h2/src/main/org/h2/expression/Parameter.java

@@ -15,7 +15,7 @@ import org.h2.value.ValueBoolean;
 import org.h2.value.ValueNull;
 
 /**
- * @author Thomas
+ * A parameter of a prepared statement.
  */
 public class Parameter extends Expression implements ParameterInterface {
 

h2/src/main/org/h2/expression/ParameterInterface.java

@@ -8,6 +8,9 @@ import java.sql.SQLException;
 
 import org.h2.value.Value;
 
+/**
+ * The interface for client side (remote) and server side parameters.
+ */
 public interface ParameterInterface {
     void setValue(Value value);
     Value getParamValue() throws SQLException;

h2/src/main/org/h2/expression/ParameterRemote.java

@@ -10,6 +10,9 @@ import org.h2.constant.ErrorCode;
 import org.h2.message.Message;
 import org.h2.value.Value;
 
+/**
+ * A client side (remote) parameter.
+ */
 public class ParameterRemote implements ParameterInterface {
 
     private Value value;

h2/src/main/org/h2/expression/Rownum.java

@@ -14,6 +14,9 @@ import org.h2.table.TableFilter;
 import org.h2.value.Value;
 import org.h2.value.ValueInt;
 
+/**
+ * Represents the ROWNUM function.
+ */
 public class Rownum extends Expression {
 
     private Prepared prepared;

h2/src/main/org/h2/expression/SequenceValue.java

@@ -15,6 +15,9 @@ import org.h2.value.Value;
 import org.h2.value.ValueInt;
 import org.h2.value.ValueLong;
 
+/**
+ * Wraps a sequence when used in a statement.
+ */
 public class SequenceValue extends Expression {
 
     private Sequence sequence;

h2/src/main/org/h2/expression/Subquery.java

@@ -18,9 +18,9 @@ import org.h2.value.ValueArray;
 import org.h2.value.ValueNull;
 
 /**
- * @author Thomas
+ * A query returning a single value.
+ * Subqueries are used inside other statements.
  */
-
 public class Subquery extends Expression {
 
     private Query query;

h2/src/main/org/h2/expression/ValueExpression.java

@@ -15,6 +15,9 @@ import org.h2.value.Value;
 import org.h2.value.ValueBoolean;
 import org.h2.value.ValueNull;
 
+/**
+ * An expression representing a constant value.
+ */
 public class ValueExpression extends Expression {
     private Value value;
 

h2/src/main/org/h2/expression/Wildcard.java

@@ -13,11 +13,11 @@ import org.h2.table.ColumnResolver;
 import org.h2.table.TableFilter;
 import org.h2.value.Value;
 
-
 /**
- * @author Thomas
+ * A wildcard expression as in SELECT * FROM TEST.
+ * This object is only used temporarily during the parsing phase, and later
+ * replaced by column expressions.
  */
-
 public class Wildcard extends Expression {
     private String schema;
     private String table;

h2/src/main/org/h2/fulltext/FullTextSettings.java

@@ -14,6 +14,9 @@ import java.util.HashSet;
 
 import org.h2.util.ObjectUtils;
 
+/**
+ * The global settings of a full text search.
+ */
 public class FullTextSettings {
 
     private static HashMap settings = new HashMap();

h2/src/main/org/h2/fulltext/IndexInfo.java

@@ -4,6 +4,9 @@
  */
 package org.h2.fulltext;
 
+/**
+ * The settings of one full text search index.
+ */
 public class IndexInfo {
     int id;
     String schemaName;

h2/src/main/org/h2/store/fs/FileSystem.java

@@ -9,7 +9,6 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.sql.SQLException;
 
-
 public abstract class FileSystem {
 
     public static final String MEMORY_PREFIX = "memFS:";