Java tutorial
/* * Copyright (C) 2007 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package android.database; import android.annotation.UnsupportedAppUsage; import android.os.Build; import java.util.ArrayList; /** * A mutable cursor implementation backed by an array of {@code Object}s. Use * {@link #newRow()} to add rows. Automatically expands internal capacity * as needed. */ public class MatrixCursor extends AbstractCursor { private final String[] columnNames; @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 115609023) private Object[] data; @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 115609023) private int rowCount = 0; private final int columnCount; /** * Constructs a new cursor with the given initial capacity. * * @param columnNames names of the columns, the ordering of which * determines column ordering elsewhere in this cursor * @param initialCapacity in rows */ public MatrixCursor(String[] columnNames, int initialCapacity) { this.columnNames = columnNames; this.columnCount = columnNames.length; if (initialCapacity < 1) { initialCapacity = 1; } this.data = new Object[columnCount * initialCapacity]; } /** * Constructs a new cursor. * * @param columnNames names of the columns, the ordering of which * determines column ordering elsewhere in this cursor */ public MatrixCursor(String[] columnNames) { this(columnNames, 16); } /** * Gets value at the given column for the current row. */ @UnsupportedAppUsage private Object get(int column) { if (column < 0 || column >= columnCount) { throw new CursorIndexOutOfBoundsException( "Requested column: " + column + ", # of columns: " + columnCount); } if (mPos < 0) { throw new CursorIndexOutOfBoundsException("Before first row."); } if (mPos >= rowCount) { throw new CursorIndexOutOfBoundsException("After last row."); } return data[mPos * columnCount + column]; } /** * Adds a new row to the end and returns a builder for that row. Not safe * for concurrent use. * * @return builder which can be used to set the column values for the new * row */ public RowBuilder newRow() { final int row = rowCount++; final int endIndex = rowCount * columnCount; ensureCapacity(endIndex); return new RowBuilder(row); } /** * Adds a new row to the end with the given column values. Not safe * for concurrent use. * * @throws IllegalArgumentException if {@code columnValues.length != * columnNames.length} * @param columnValues in the same order as the the column names specified * at cursor construction time */ public void addRow(Object[] columnValues) { if (columnValues.length != columnCount) { throw new IllegalArgumentException( "columnNames.length = " + columnCount + ", columnValues.length = " + columnValues.length); } int start = rowCount++ * columnCount; ensureCapacity(start + columnCount); System.arraycopy(columnValues, 0, data, start, columnCount); } /** * Adds a new row to the end with the given column values. Not safe * for concurrent use. * * @throws IllegalArgumentException if {@code columnValues.size() != * columnNames.length} * @param columnValues in the same order as the the column names specified * at cursor construction time */ public void addRow(Iterable<?> columnValues) { int start = rowCount * columnCount; int end = start + columnCount; ensureCapacity(end); if (columnValues instanceof ArrayList<?>) { addRow((ArrayList<?>) columnValues, start); return; } int current = start; Object[] localData = data; for (Object columnValue : columnValues) { if (current == end) { // TODO: null out row? throw new IllegalArgumentException("columnValues.size() > columnNames.length"); } localData[current++] = columnValue; } if (current != end) { // TODO: null out row? throw new IllegalArgumentException("columnValues.size() < columnNames.length"); } // Increase row count here in case we encounter an exception. rowCount++; } /** Optimization for {@link ArrayList}. */ private void addRow(ArrayList<?> columnValues, int start) { int size = columnValues.size(); if (size != columnCount) { throw new IllegalArgumentException( "columnNames.length = " + columnCount + ", columnValues.size() = " + size); } rowCount++; Object[] localData = data; for (int i = 0; i < size; i++) { localData[start + i] = columnValues.get(i); } } /** Ensures that this cursor has enough capacity. */ private void ensureCapacity(int size) { if (size > data.length) { Object[] oldData = this.data; int newSize = data.length * 2; if (newSize < size) { newSize = size; } this.data = new Object[newSize]; System.arraycopy(oldData, 0, this.data, 0, oldData.length); } } /** * Builds a row of values using either of these approaches: * <ul> * <li>Values can be added with explicit column ordering using * {@link #add(Object)}, which starts from the left-most column and adds one * column value at a time. This follows the same ordering as the column * names specified at cursor construction time. * <li>Column and value pairs can be offered for possible inclusion using * {@link #add(String, Object)}. If the cursor includes the given column, * the value will be set for that column, otherwise the value is ignored. * This approach is useful when matching data to a custom projection. * </ul> * Undefined values are left as {@code null}. */ public class RowBuilder { private final int row; private final int endIndex; private int index; RowBuilder(int row) { this.row = row; this.index = row * columnCount; this.endIndex = index + columnCount; } /** * Sets the next column value in this row. * * @throws CursorIndexOutOfBoundsException if you try to add too many * values * @return this builder to support chaining */ public RowBuilder add(Object columnValue) { if (index == endIndex) { throw new CursorIndexOutOfBoundsException("No more columns left."); } data[index++] = columnValue; return this; } /** * Offer value for possible inclusion if this cursor defines the given * column. Columns not defined by the cursor are silently ignored. * * @return this builder to support chaining */ public RowBuilder add(String columnName, Object value) { for (int i = 0; i < columnNames.length; i++) { if (columnName.equals(columnNames[i])) { data[(row * columnCount) + i] = value; } } return this; } } // AbstractCursor implementation. @Override public int getCount() { return rowCount; } @Override public String[] getColumnNames() { return columnNames; } @Override public String getString(int column) { Object value = get(column); if (value == null) return null; return value.toString(); } @Override public short getShort(int column) { Object value = get(column); if (value == null) return 0; if (value instanceof Number) return ((Number) value).shortValue(); return Short.parseShort(value.toString()); } @Override public int getInt(int column) { Object value = get(column); if (value == null) return 0; if (value instanceof Number) return ((Number) value).intValue(); return Integer.parseInt(value.toString()); } @Override public long getLong(int column) { Object value = get(column); if (value == null) return 0; if (value instanceof Number) return ((Number) value).longValue(); return Long.parseLong(value.toString()); } @Override public float getFloat(int column) { Object value = get(column); if (value == null) return 0.0f; if (value instanceof Number) return ((Number) value).floatValue(); return Float.parseFloat(value.toString()); } @Override public double getDouble(int column) { Object value = get(column); if (value == null) return 0.0d; if (value instanceof Number) return ((Number) value).doubleValue(); return Double.parseDouble(value.toString()); } @Override public byte[] getBlob(int column) { Object value = get(column); return (byte[]) value; } @Override public int getType(int column) { return DatabaseUtils.getTypeOfObject(get(column)); } @Override public boolean isNull(int column) { return get(column) == null; } }