Beef.java

/**
 * Copyright 2007 The Apache Software Foundation
 *
 * 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 net.paoding.analysis.knife;

/**
 * {@link Beef}是要被庖丁“解”的“牛骨肉”，是对文本字符流的高效封装，可以从中读取指定位置的字符。
 * <p>
 * {@link Beef}和{@link String}对象的不同之处在于：<br>
 * {@link Beef}共享输入的char数组，{@link String}的策略是对共享数组进行克隆，克隆损耗了性能。<br>
 * 同时，{@link Beef}在 {@link #charAt(int)}方法还进行对字符的预处理，使返回时符合规则:1)toLowerCase
 * 2)全角转半角等
 * <p>
 * 
 * @author Zhiliang Wang [qieqie.wang@gmail.com]
 * 
 * @since 1.0
 * 
 */
public class Beef implements CharSequence {

	// -------------------------------------------------

	/**
	 * 文本字符数组
	 */
	private final char[] value;

	/**
	 * 字符开始位置，即charAt(i)返回value[offset+i]字符
	 */
	private int offset;

	/**
	 * 从offset位置开始的字符数
	 */
	private int count;

	/** Cache the hash code for the beef */
	private int hash; // Default to 0

	// -------------------------------------------------

	/**
	 * 构造函数
	 * 
	 * @param body
	 *            被本对象中直接拥有的文本字符数组
	 * @param offset
	 *            字符开始位置，即get(i)返回body[offset+i]字符
	 * @param count
	 *            从offset位置开始的字符数
	 */
	public Beef(char[] value, int offset, int count) {
		this.value = value;
		set(offset, count);
	}

	// -------------------------------------------------

	public void set(int offset, int count) {
        if (offset < 0) {
            throw new StringIndexOutOfBoundsException(offset);
        }
        if (count < 0) {
            throw new StringIndexOutOfBoundsException(count);
        }
        if (offset > value.length - count) {
            throw new StringIndexOutOfBoundsException(offset + count);
        }
		this.offset = offset;
		this.count = count;
	}

	public char[] getValue() {
		return value;
	}


	public int getCount() {
		return count;
	}

	public int getOffset() {
		return offset;
	}

	// -------------------------------------------------
	
	/**
	 * 获取指定位置的字符。返回之前将被预处理：1)toLowerCase，2)全角转半角等
	 */
	public char charAt(int index) {
		if (index >= 0 && index < count) {
			char src = value[offset + index];
			if (src > 65280 && src < 65375) {
				src = (char) (src - 65248);
				value[offset + index] = src;
			}
			if (src >= 'A' && src <= 'Z') {
				src += 32;
				value[offset + index] = src;
			} else if (src == 12288) {
				src = 32;
				value[offset + index] = 32;
			}
			return src;
		}
		return (char) -1;
	}

	public int length() {
		return count;
	}

	public CharSequence subSequence(int start, int end) {
		return new String(value, offset + start, end - start);
	}

	// -------------------------------------------------
	
	public String toString() {
		return new String(value, offset, count);
	}

	public int hashCode() {
		int h = hash;
		if (h == 0) {
			int off = offset;
			char val[] = value;
			int len = count;

			for (int i = 0; i < len; i++) {
				h = 31 * h + val[off++];
			}
			hash = h;
		}
		return h;
	}

}