StringCharacterIterator.java

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/*
 * (C) Copyright Taligent, Inc. 1996, 1997 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996 - 1998 - All Rights Reserved
 *
 * The original version of this source code and documentation
 * is copyrighted and owned by Taligent, Inc., a wholly-owned
 * subsidiary of IBM. These materials are provided under terms
 * of a License Agreement between Taligent and Sun. This technology
 * is protected by multiple US and International patents.
 *
 * This notice and attribution to Taligent may not be removed.
 * Taligent is a registered trademark of Taligent, Inc.
 *
 */

package java.text;

/**
 * StringCharacterIterator implements the CharacterIterator protocol for a String.
 * The StringCharacterIterator class iterates over the entire String.
 *
 * @see CharacterIterator
 * @since 1.1
 */
// StringCharacterIterator实现了CharacterIterator接口（协议），用来遍历非空String。
public final class StringCharacterIterator implements CharacterIterator {
    
    private String text;// 待遍历文本
    
    private int begin;  // 游标pos的起点
    private int end;    // 游标pos的终点
    private int pos;    // 游标pos的迭代范围是[begin, end]，且在end时，需要标记为DONE，表示结束/异常/错误
    
    /**
     * Constructs an iterator with an initial index of 0.
     *
     * @param text the {@code String} to be iterated over
     */
    // 为非空String初始化一个字符迭代器，并设置迭代范围为[0, length]，游标位置为0
    public StringCharacterIterator(String text) {
        this(text, 0);
    }
    
    /**
     * Constructs an iterator with the specified initial index.
     *
     * @param text The String to be iterated over
     * @param pos  Initial iterator position
     */
    // 为非空String初始化一个字符迭代器，并设置可迭代范围为[0, length]，游标当前位置pos
    public StringCharacterIterator(String text, int pos) {
        this(text, 0, text.length(), pos);
    }
    
    /**
     * Constructs an iterator over the given range of the given string, with the index set at the specified position.
     *
     * @param text  The String to be iterated over
     * @param begin Index of the first character
     * @param end   Index of the character following the last character
     * @param pos   Initial iterator position
     */
    // 为非空String初始化一个字符迭代器，并设置可迭代范围为[begin, end]，游标当前位置pos
    public StringCharacterIterator(String text, int begin, int end, int pos) {
        if(text == null)
            throw new NullPointerException();
        this.text = text;
        
        if(begin < 0 || begin > end || end > text.length())
            throw new IllegalArgumentException("Invalid substring range");
        
        if(pos < begin || pos > end)
            throw new IllegalArgumentException("Invalid position");
        
        this.begin = begin;
        this.end = end;
        this.pos = pos;
    }
    
    /**
     * Reset this iterator to point to a new string.
     * This package-visible method is used by other java.text classes
     * that want to avoid allocating new StringCharacterIterator objects every time their setText method is called.
     *
     * @param text The String to be iterated over
     *
     * @since 1.2
     */
    // 为迭代器关联新的非空文本，并将可迭代范围重置为[0, length]，游标重置为0
    public void setText(String text) {
        if(text == null)
            throw new NullPointerException();
        this.text = text;
        this.begin = 0;
        this.end = text.length();
        this.pos = 0;
    }
    
    /**
     * Implements CharacterIterator.setIndex() for String.
     *
     * @see CharacterIterator#setIndex
     */
    // 重置游标为p，并返回该处的char。如果游标指向了终点end，则返回无效字符DONE。
    public char setIndex(int p) {
        if(p < begin || p > end)
            throw new IllegalArgumentException("Invalid index");
        pos = p;
        return current();
    }
    
    /**
     * Implements CharacterIterator.first() for String.
     *
     * @see CharacterIterator#first
     */
    // 设置游标到第一个有效字符位置，并返回该char。
    public char first() {
        pos = begin;
        return current();
    }
    
    /**
     * Implements CharacterIterator.last() for String.
     *
     * @see CharacterIterator#last
     */
    // 设置游标到最后一个有效字符位置，并返回该char。
    public char last() {
        if(end != begin) {
            pos = end - 1;
        } else {
            pos = end;
        }
        return current();
    }
    
    /**
     * Implements CharacterIterator.current() for String.
     *
     * @see CharacterIterator#current
     */
    // 返回游标当前指向的char。如果游标指向了终点end，则返回无效字符DONE。
    public char current() {
        if(pos >= begin && pos < end) {
            return text.charAt(pos);
        } else {
            return DONE;
        }
    }
    
    /**
     * Implements CharacterIterator.previous() for String.
     *
     * @see CharacterIterator#previous
     */
    // 如果游标未到起点，则先前移游标，再返回指向的char。否则游标位置不变，且返回DONE。
    public char previous() {
        if(pos > begin) {
            pos--;
            return text.charAt(pos);
        } else {
            return DONE;
        }
    }
    
    /**
     * Implements CharacterIterator.next() for String.
     *
     * @see CharacterIterator#next
     */
    // 如果游标未到终点，则先后移游标，再返回指向的char。否则游标设置在终点，且返回DONE。
    public char next() {
        if(pos < end - 1) {
            pos++;
            return text.charAt(pos);
        } else {
            pos = end;
            return DONE;
        }
    }
    
    /**
     * Implements CharacterIterator.getBeginIndex() for String.
     *
     * @see CharacterIterator#getBeginIndex
     */
    // 返回游标起点
    public int getBeginIndex() {
        return begin;
    }
    
    /**
     * Implements CharacterIterator.getEndIndex() for String.
     *
     * @see CharacterIterator#getEndIndex
     */
    // 返回游标终点
    public int getEndIndex() {
        return end;
    }
    
    /**
     * Implements CharacterIterator.getIndex() for String.
     *
     * @see CharacterIterator#getIndex
     */
    // 返回游标当前位置（索引）
    public int getIndex() {
        return pos;
    }
    
    /**
     * Creates a copy of this iterator.
     *
     * @return A copy of this
     */
    // 创建当前迭代器的一份复制品
    public Object clone() {
        try {
            StringCharacterIterator other = (StringCharacterIterator) super.clone();
            return other;
        } catch(CloneNotSupportedException e) {
            throw new InternalError(e);
        }
    }
    
    /**
     * Compares the equality of two StringCharacterIterator objects.
     *
     * @param obj the StringCharacterIterator object to be compared with.
     *
     * @return true if the given obj is the same as this
     * StringCharacterIterator object; false otherwise.
     */
    public boolean equals(Object obj) {
        if(this == obj) {
            return true;
        }
        
        if(!(obj instanceof StringCharacterIterator)) {
            return false;
        }
        
        StringCharacterIterator that = (StringCharacterIterator) obj;
        
        if(hashCode() != that.hashCode()) {
            return false;
        }
        if(!text.equals(that.text)) {
            return false;
        }
        if(pos != that.pos || begin != that.begin || end != that.end) {
            return false;
        }
        
        return true;
    }
    
    /**
     * Computes a hashcode for this iterator.
     *
     * @return A hash code
     */
    public int hashCode() {
        return text.hashCode() ^ pos ^ begin ^ end;
    }
}