欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页

读AbstractStringBuilder源码

程序员文章站 2022-03-19 11:36:21
...
//该类是StringBuilder和StringBuffer基类实现了Appendable和CharSequence接口
//StringBuffer是线程安全的.所以就在所有方法上加上了synchronized关键字。


//先看构造函数
AbstractStringBuilder() {
    }

AbstractStringBuilder(int capacity) {
        value = new char[capacity];
    }

//返回长度
 public int length() {
        return count;
    }

//返回容量
 public int capacity() {
        return value.length;
    }

//扩容
public void ensureCapacity(int minimumCapacity) {
        if (minimumCapacity > 0)
            ensureCapacityInternal(minimumCapacity);
    }

 private void ensureCapacityInternal(int minimumCapacity) {
        if (minimumCapacity - value.length > 0)
            expandCapacity(minimumCapacity);
    }

//扩容
void expandCapacity(int minimumCapacity) {
        int newCapacity = value.length * 2 + 2;
        if (newCapacity - minimumCapacity < 0)
            newCapacity = minimumCapacity;
        if (newCapacity < 0) {
            if (minimumCapacity < 0) // overflow
                throw new OutOfMemoryError();
            newCapacity = Integer.MAX_VALUE;
        }
        value = Arrays.copyOf(value, newCapacity);
    }

//将value变为当前大小
public void trimToSize() {
        if (count < value.length) {
            value = Arrays.copyOf(value, count);
        }
    }

//设置当前长度
 public void setLength(int newLength) {
        if (newLength < 0)
            throw new StringIndexOutOfBoundsException(newLength);
        ensureCapacityInternal(newLength);

        if (count < newLength) {
            for (; count < newLength; count++)
                value[count] = '\0';
        } else {
            count = newLength;
        }
    }

//返回index位置的char值
public char charAt(int index) {
        if ((index < 0) || (index >= count))
            throw new StringIndexOutOfBoundsException(index);
        return value[index];
    }


//返回index位置的unicode代码点
public int codePointAt(int index) {
        if ((index < 0) || (index >= count)) {
            throw new StringIndexOutOfBoundsException(index);
        }
        return Character.codePointAt(value, index);
    }

//返回index位置之前的unicode代码点
 public int codePointBefore(int index) {
        int i = index - 1;
        if ((i < 0) || (i >= count)) {
            throw new StringIndexOutOfBoundsException(index);
        }
        return Character.codePointBefore(value, index);
    }


//返回beginIndex,endIndex之间的unicode代码点数
public int codePointCount(int beginIndex, int endIndex) {
        if (beginIndex < 0 || endIndex > count || beginIndex > endIndex) {
            throw new IndexOutOfBoundsException();
        }
        return Character.codePointCountImpl(value, beginIndex, endIndex-beginIndex);
    }

 public int offsetByCodePoints(int index, int codePointOffset) {
        if (index < 0 || index > count) {
            throw new IndexOutOfBoundsException();
        }
        return Character.offsetByCodePointsImpl(value, 0, count,
                                                index, codePointOffset);
    }


//复制当前序列到dst
public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
    {
        if (srcBegin < 0)
            throw new StringIndexOutOfBoundsException(srcBegin);
        if ((srcEnd < 0) || (srcEnd > count))
            throw new StringIndexOutOfBoundsException(srcEnd);
        if (srcBegin > srcEnd)
            throw new StringIndexOutOfBoundsException("srcBegin > srcEnd");
        System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin);
    }


//设置index位置的char值
public void setCharAt(int index, char ch) {
        if ((index < 0) || (index >= count))
            throw new StringIndexOutOfBoundsException(index);
        value[index] = ch;
    }

//将Object的字符串表示形式添加到序列中
 public AbstractStringBuilder append(Object obj) {
        return append(String.valueOf(obj));
    }

public AbstractStringBuilder append(String str) {
        if (str == null) str = "null";
        int len = str.length();
        ensureCapacityInternal(count + len);
	//把自己复制到此序列中
        str.getChars(0, len, value, count);
        count += len;
        return this;
    }

//将StringBuffer添加到序列中
public AbstractStringBuilder append(StringBuffer sb) {
        if (sb == null)
            return append("null");
        int len = sb.length();
        ensureCapacityInternal(count + len);
        sb.getChars(0, len, value, count);
        count += len;
        return this;
    }

//将CharSequence添加到序列中
 public AbstractStringBuilder append(CharSequence s) {
        if (s == null)
            s = "null";
        if (s instanceof String)
            return this.append((String)s);
        if (s instanceof StringBuffer)
            return this.append((StringBuffer)s);
        return this.append(s, 0, s.length());
    }

//将CharSequence从start到end间的字符添加到序列中
public AbstractStringBuilder append(CharSequence s, int start, int end) {
        if (s == null)
            s = "null";
        if ((start < 0) || (start > end) || (end > s.length()))
            throw new IndexOutOfBoundsException(
                "start " + start + ", end " + end + ", s.length() "
                + s.length());
        int len = end - start;
        ensureCapacityInternal(count + len);
        for (int i = start, j = count; i < end; i++, j++)
            value[j] = s.charAt(i);
        count += len;
        return this;
    }

//将char[]添加到序列中
public AbstractStringBuilder append(char[] str) {
        int len = str.length;
        ensureCapacityInternal(count + len);
        System.arraycopy(str, 0, value, count, len);
        count += len;
        return this;
    }

public AbstractStringBuilder append(char str[], int offset, int len) {
        if (len > 0)                // let arraycopy report AIOOBE for len < 0
            ensureCapacityInternal(count + len);
        System.arraycopy(str, offset, value, count, len);
        count += len;
        return this;
    }


 public AbstractStringBuilder append(boolean b) {
        if (b) {
            ensureCapacityInternal(count + 4);
            value[count++] = 't';
            value[count++] = 'r';
            value[count++] = 'u';
            value[count++] = 'e';
        } else {
            ensureCapacityInternal(count + 5);
            value[count++] = 'f';
            value[count++] = 'a';
            value[count++] = 'l';
            value[count++] = 's';
            value[count++] = 'e';
        }
        return this;
    }

public AbstractStringBuilder append(char c) {
        ensureCapacityInternal(count + 1);
        value[count++] = c;
        return this;
    }


//删掉start到end之间的字符
  public AbstractStringBuilder delete(int start, int end) {
        if (start < 0)
            throw new StringIndexOutOfBoundsException(start);
        if (end > count)
            end = count;
        if (start > end)
            throw new StringIndexOutOfBoundsException();
        int len = end - start;
        if (len > 0) {
	    //移动字符
            System.arraycopy(value, start+len, value, start, count-end);
            count -= len;
        }
        return this;
    }


public AbstractStringBuilder appendCodePoint(int codePoint) {
        final int count = this.count;

        if (Character.isBmpCodePoint(codePoint)) {
            ensureCapacityInternal(count + 1);
            value[count] = (char) codePoint;
            this.count = count + 1;
        } else if (Character.isValidCodePoint(codePoint)) {
            ensureCapacityInternal(count + 2);
            Character.toSurrogates(codePoint, value, count);
            this.count = count + 2;
        } else {
            throw new IllegalArgumentException();
        }
        return this;
    }

//删除指定位置的字符
public AbstractStringBuilder deleteCharAt(int index) {
        if ((index < 0) || (index >= count))
            throw new StringIndexOutOfBoundsException(index);
        System.arraycopy(value, index+1, value, index, count-index-1);
        count--;
        return this;
    }


public AbstractStringBuilder replace(int start, int end, String str) {
        if (start < 0)
            throw new StringIndexOutOfBoundsException(start);
        if (start > count)
            throw new StringIndexOutOfBoundsException("start > length()");
        if (start > end)
            throw new StringIndexOutOfBoundsException("start > end");

        if (end > count)
            end = count;
        int len = str.length();
	//计算新长度
        int newCount = count + len - (end - start);
        ensureCapacityInternal(newCount);
        //先移动整个数组
        System.arraycopy(value, end, value, start + len, count - end);
        //将str复制到数组中
	str.getChars(value, start);
        count = newCount;
        return this;
    }


//从start位置返回新的字符串
public String substring(int start) {
        return substring(start, count);
    }

public CharSequence subSequence(int start, int end) {
        return substring(start, end);
    }

 public String substring(int start, int end) {
        if (start < 0)
            throw new StringIndexOutOfBoundsException(start);
        if (end > count)
            throw new StringIndexOutOfBoundsException(end);
        if (start > end)
            throw new StringIndexOutOfBoundsException(end - start);
        return new String(value, start, end - start);
    }

//在指定位置插入obj的string表示形式
public AbstractStringBuilder insert(int offset, Object obj) {
        return insert(offset, String.valueOf(obj));
    }


public AbstractStringBuilder insert(int offset, String str) {
        if ((offset < 0) || (offset > length()))
            throw new StringIndexOutOfBoundsException(offset);
        if (str == null)
            str = "null";
        int len = str.length();
        ensureCapacityInternal(count + len);
	//先移动
        System.arraycopy(value, offset, value, offset + len, count - offset);
        //再添加
	str.getChars(value, offset);
        count += len;
        return this;
    }


public AbstractStringBuilder insert(int index, char[] str, int offset,
                                        int len)
    {
        if ((index < 0) || (index > length()))
            throw new StringIndexOutOfBoundsException(index);
        if ((offset < 0) || (len < 0) || (offset > str.length - len))
            throw new StringIndexOutOfBoundsException(
                "offset " + offset + ", len " + len + ", str.length "
                + str.length);
        ensureCapacityInternal(count + len);
	//先复制,数组中间空出str的位置
        System.arraycopy(value, index, value, index + len, count - index);
	//再次复制
        System.arraycopy(str, offset, value, index, len);
        count += len;
        return this;
    }

 public AbstractStringBuilder insert(int offset, char[] str) {
        if ((offset < 0) || (offset > length()))
            throw new StringIndexOutOfBoundsException(offset);
        int len = str.length;
        ensureCapacityInternal(count + len);
        System.arraycopy(value, offset, value, offset + len, count - offset);
        System.arraycopy(str, 0, value, offset, len);
        count += len;
        return this;
    }


 public AbstractStringBuilder insert(int dstOffset, CharSequence s) {
        if (s == null)
            s = "null";
        if (s instanceof String)
            return this.insert(dstOffset, (String)s);
        return this.insert(dstOffset, s, 0, s.length());
    }

 public AbstractStringBuilder insert(int dstOffset, CharSequence s,
                                         int start, int end) {
        if (s == null)
            s = "null";
        if ((dstOffset < 0) || (dstOffset > this.length()))
            throw new IndexOutOfBoundsException("dstOffset "+dstOffset);
        if ((start < 0) || (end < 0) || (start > end) || (end > s.length()))
            throw new IndexOutOfBoundsException(
                "start " + start + ", end " + end + ", s.length() "
                + s.length());
        int len = end - start;
        ensureCapacityInternal(count + len);
        System.arraycopy(value, dstOffset, value, dstOffset + len,
                         count - dstOffset);
        for (int i=start; i<end; i++)
            value[dstOffset++] = s.charAt(i);
        count += len;
        return this;
    }

//返回包含字符串的字符串
public int indexOf(String str) {
        return indexOf(str, 0);
    }

 public int indexOf(String str, int fromIndex) {
        return String.indexOf(value, 0, count,
                              str.toCharArray(), 0, str.length(), fromIndex);
    }

//从尾巴开始搜索
public int lastIndexOf(String str) {
        return lastIndexOf(str, count);
    }

 public int lastIndexOf(String str, int fromIndex) {
        return String.lastIndexOf(value, 0, count,
                              str.toCharArray(), 0, str.length(), fromIndex);
    }



相关标签: java