07 java.lang.StringBuilder

StringBuilder

2015.01.15
By 970655147

如果大家有过字符串拼接的经验的话, 可能对于这个类不会陌生, 因为直接使用String拼接多个字符串的话, 开销略大, 那么这种场景下StringBuilder/ StringBuffer, 就闪亮登场了

start ->

声明

, 大家可以看看注释

/**
* A mutable sequence of characters.  This class provides an API compatible
* with <code>StringBuffer</code>, but with no guarantee of synchronization.
* This class is designed for use as a drop-in replacement for
* <code>StringBuffer</code> in places where the string buffer was being
* used by a single thread (as is generally the case).   Where possible,
* it is recommended that this class be used in preference to
* <code>StringBuffer</code> as it will be faster under most implementations.
*
* <p>The principal operations on a <code>StringBuilder</code> are the
* <code>append</code> and <code>insert</code> methods, which are
* overloaded so as to accept data of any type. Each effectively
* converts a given datum to a string and then appends or inserts the
* characters of that string to the string builder. The
* <code>append</code> method always adds these characters at the end
* of the builder; the <code>insert</code> method adds the characters at
* a specified point.
* <p>
* For example, if <code>z</code> refers to a string builder object
* whose current contents are "<code>start</code>", then
* the method call <code>z.append("le")</code> would cause the string
* builder to contain "<code>startle</code>", whereas
* <code>z.insert(4, "le")</code> would alter the string builder to
* contain "<code>starlet</code>".
* <p>
* In general, if sb refers to an instance of a <code>StringBuilder</code>,
* then <code>sb.append(x)</code> has the same effect as
* <code>sb.insert(sb.length(), x)</code>.
*
* Every string builder has a capacity. As long as the length of the
* character sequence contained in the string builder does not exceed
* the capacity, it is not necessary to allocate a new internal
* buffer. If the internal buffer overflows, it is automatically made larger.
*
* <p>Instances of <code>StringBuilder</code> are not safe for
* use by multiple threads. If such synchronization is required then it is
* recommended that {@link java.lang.StringBuffer} be used.
*
* @author      Michael McCloskey
* @see         java.lang.StringBuffer
* @see         java.lang.String
* @since       1.5
*/
public final class StringBuilder
extends AbstractStringBuilder
implements java.io.Serializable, CharSequence

StringBuilder. append(Object/ String/ StringBuilder/ CharSequence obj)

public StringBuilder append(Object obj) {
return append(String.valueOf(obj));
}

public StringBuilder append(String str) {
super.append(str);
return this;
}

public StringBuilder append(StringBuffer sb) {
super.append(sb);
return this;
}

public StringBuilder 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);
if (s instanceof StringBuilder)
return this.append((StringBuilder)s);
return this.append(s, 0, s.length());
}

public StringBuilder append(CharSequence s, int start, int end) {
super.append(s, start, end);
return this;
}

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;
// 确保空间足够
ensureCapacityInternal(count + len);
// 拼接数据
for (int i = start, j = count; i < end; i++, j++)
value[j] = s.charAt(i);
count += len;
return this;
}

public AbstractStringBuilder append(String str) {
if (str == null) str = "null";
int len = str.length();
// 确保value能存放append str 不够则扩容
ensureCapacityInternal(count + len);
// 将str的字符拼接到value后面
str.getChars(0, len, value, count);
count += len;
return this;
}

private void ensureCapacityInternal(int minimumCapacity) {
// overflow-conscious code
// 如果需求的minCapacity大于value.length 则扩容
if (minimumCapacity - value.length > 0)
expandCapacity(minimumCapacity);
}

void expandCapacity(int minimumCapacity) {
// 默认的扩容机制
int newCapacity = value.length * 2 + 2;
// 如果默认的扩容小了 则扩大至minCapacity
if (newCapacity - minimumCapacity < 0)
newCapacity = minimumCapacity;
if (newCapacity < 0) {
if (minimumCapacity < 0) // overflow
throw new OutOfMemoryError();
newCapacity = Integer.MAX_VALUE;
}
// 拷贝value的数据到新的Array中
value = Arrays.copyOf(value, newCapacity);
}

StringBuilder. append(char[] str)

public StringBuilder append(char[] str) {
super.append(str);
return this;
}

public AbstractStringBuilder append(char[] str) {
int len = str.length;
// 确保空间，拼接数据
ensureCapacityInternal(count + len);
System.arraycopy(str, 0, value, count, len);
count += len;
return this;
}

StringBuilder. append(char[] str, int offset, int len)

public StringBuilder append(char[] str, int offset, int len) {
super.append(str, offset, 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;
}

StringBuilder. appedn(boolean/ int/long// float/ double b)

public StringBuilder append(boolean b) {
super.append(b);
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 StringBuilder append(char c) {
super.append(c);
return this;
}

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

public StringBuilder append(int i) {
super.append(i);
return this;
}

public AbstractStringBuilder append(int i) {
if (i == Integer.MIN_VALUE) {
append("-2147483648");
return this;
}
// 存放i需要的长度，负数+1(“-”)
int appendedLength = (i < 0) ? Integer.stringSize(-i) + 1
: Integer.stringSize(i);
int spaceNeeded = count + appendedLength;
ensureCapacityInternal(spaceNeeded);
// 填充i的字符数据到value
Integer.getChars(i, spaceNeeded, value);
count = spaceNeeded;
return this;
}

public StringBuilder append(long lng) {
super.append(lng);
return this;
}

public AbstractStringBuilder append(long l) {
if (l == Long.MIN_VALUE) {
append("-9223372036854775808");
return this;
}
int appendedLength = (l < 0) ? Long.stringSize(-l) + 1
: Long.stringSize(l);
int spaceNeeded = count + appendedLength;
ensureCapacityInternal(spaceNeeded);
Long.getChars(l, spaceNeeded, value);
count = spaceNeeded;
return this;
}

public StringBuilder append(float f) {
super.append(f);
return this;
}

public AbstractStringBuilder append(float f) {
new FloatingDecimal(f).appendTo(this);
return this;
}

public StringBuilder append(double d) {
super.append(d);
return this;
}

public AbstractStringBuilder append(double d) {
new FloatingDecimal(d).appendTo(this);
return this;
}

StringBuilder. appendCodePoint(int codePoint)

public StringBuilder appendCodePoint(int codePoint) {
super.appendCodePoint(codePoint);
return this;
}

public AbstractStringBuilder appendCodePoint(int codePoint) {
final int count = this.count;
// 判定codePoint是否在Basic Multilingual Plane范围内，如果是的话 添加1个字符即可
if (Character.isBmpCodePoint(codePoint)) {
ensureCapacityInternal(count + 1);
value[count] = (char) codePoint;
this.count = count + 1;
// 判断codePoint是否是一个合法Unicode
} else if (Character.isValidCodePoint(codePoint)) {
ensureCapacityInternal(count + 2);
Character.toSurrogates(codePoint, value, count);
this.count = count + 2;
} else {
throw new IllegalArgumentException();
}
return this;
}

public static boolean isBmpCodePoint(int codePoint) {
return codePoint >>> 16 == 0;
// Optimized form of:
//     codePoint >= MIN_VALUE && codePoint <= MAX_VALUE
// We consistently use logical shift (>>>) to facilitate
// additional runtime optimizations.
}

public static boolean isValidCodePoint(int codePoint) {
// Optimized form of:
//     codePoint >= MIN_CODE_POINT && codePoint <= MAX_CODE_POINT
int plane = codePoint >>> 16;
return plane < ((MAX_CODE_POINT + 1) >>> 16);
}

StringBuilder. delete(int start, int end)

public StringBuilder delete(int start, int end) {
super.delete(start, end);
return this;
}

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) {
// 将start+len的字符移动到start处 迭代count-end次
System.arraycopy(value, start+len, value, start, count-end);
count -= len;
}
return this;
}

StringBuilder. deleteCharAt(int index)

public StringBuilder deleteCharAt(int index) {
super.deleteCharAt(index);
return this;
}

public AbstractStringBuilder deleteCharAt(int index) {
if ((index < 0) || (index >= count))
throw new StringIndexOutOfBoundsException(index);
// 将index+1的字符移动到index处 迭代count-index-1次
System.arraycopy(value, index+1, value, index, count-index-1);
count--;
return this;
}

StringBuilder. replace(int start, int end, String str)

public StringBuilder replace(int start, int end, String str) {
super.replace(start, end, str);
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();
int newCount = count + len - (end - start);
ensureCapacityInternal(newCount);
// 将index+1的字符移动到start + len处 迭代count-end次
// start –> start+len 处的空间留给str
System.arraycopy(value, end, value, start + len, count - end);
// 填充str的数据 start–> start+len
str.getChars(value, start);
count = newCount;
return this;
}

StringBuilder. insert(int index, char[] str, int offset,int len)

public StringBuilder insert(int index, char[] str, int offset,int len)
{
super.insert(index, str, offset, 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);
// 将index处的字符移动到index+len处 迭代count-index次
System.arraycopy(value, index, value, index + len, count - index);
// 将str的字符移动到value的index处 完成插入数据
System.arraycopy(str, offset, value, index, len);
count += len;
return this;
}

StringBuilder. insert(int offset, Object obj)

public StringBuilder insert(int offset, Object obj) {
return insert(offset, String.valueOf(obj));
}

public StringBuilder insert(int offset, String str) {
super.insert(offset, str);
return this;
}

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);
// 将offset处的字符移动到offset+str.length()处 迭代count-offset次
System.arraycopy(value, offset, value, offset + len, count - offset);
// 填充str的字符数据
str.getChars(value, offset);
count += len;
return this;
}

StringBuilder. insert(int offset, char[] str)

public StringBuilder insert(int offset, char[] str) {
super.insert(offset, str);
return this;
}

public AbstractStringBuilder insert(int offset, char[]/ CharSequence str) {
if ((offset < 0) || (offset > length()))
throw new StringIndexOutOfBoundsException(offset);
int len = str.length;
ensureCapacityInternal(count + len);
// 将offset处的字符移动到offset+str.length()处 迭代count-offset次, 填充str的字符数据
System.arraycopy(value, offset, value, offset + len, count - offset);
System.arraycopy(str, 0, value, offset, len);
count += len;
return this;
}

public StringBuilder 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 StringBuilder insert(int dstOffset, CharSequence s, int start, int end)
{
super.insert(dstOffset, s, start, end);
return this;
}

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);
// 将offset处的字符移动到offset+len处 迭代count-offset次, 填充str的字符数据
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;
}

StringBuilder. insert(int offset, boolean/ int/ long/ float/ double b)

public StringBuilder insert(int offset, boolean b) {
super.insert(offset, b);
return this;
}

public AbstractStringBuilder insert(int offset, boolean b) {
return insert(offset, String.valueOf(b));
}

public StringBuilder insert(int offset, char c) {
super.insert(offset, c);
return this;
}

public AbstractStringBuilder insert(int offset, char c) {
ensureCapacityInternal(count + 1);
System.arraycopy(value, offset, value, offset + 1, count - offset);
value[offset] = c;
count += 1;
return this;
}

public StringBuilder insert(int offset, int i) {
return insert(offset, String.valueOf(i));
}

public StringBuilder insert(int offset, long l) {
return insert(offset, String.valueOf(l));
}

public StringBuilder insert(int offset, float f) {
return insert(offset, String.valueOf(f));
}

public StringBuilder insert(int offset, double d) {
return insert(offset, String.valueOf(d));
}

StringBuilder. indexOf(String str)

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);
}

StringBuilder. lastIndexOf(String str)

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);
}

StringBuilder. reverse()

public StringBuilder reverse() {
super.reverse();
return this;
}

public AbstractStringBuilder reverse() {
boolean hasSurrogate = false;
int n = count - 1;
// 逆转字符  从中间开始逆转..
for (int j = (n-1) >> 1; j >= 0; --j) {
char temp = value[j];
char temp2 = value[n - j];
if (!hasSurrogate) {
hasSurrogate = (temp >= Character.MIN_SURROGATE && temp <= Character.MAX_SURROGATE)
|| (temp2 >= Character.MIN_SURROGATE && temp2 <= Character.MAX_SURROGATE);
}
value[j] = temp2;
value[n - j] = temp;
}
// 如果存在 surrogate pairs 则将其逆转回来
if (hasSurrogate) {
// Reverse back all valid surrogate pairs
for (int i = 0; i < count - 1; i++) {
char c2 = value[i];
if (Character.isLowSurrogate(c2)) {
char c1 = value[i + 1];
if (Character.isHighSurrogate(c1)) {
value[i++] = c1;
value[i] = c2;
}
}
}
}
return this;
}

StringBuilder.toString()

public String toString() {
// Create a copy, don't share the array
return new String(value, 0, count);
}

->

ok, StringBuilder 到此结束了

这个类是非常常用的也是非常重要的, 建议详详细细的分析一遍 !

StringBuffer 和StringBuilder的内容基本一致, 不过每一个业务方法都加上了synchronized关键字, 保证了线程的安全

资源下载 : http://download.csdn.net/detail/u011039332/9051805

注 : 因为作者的水平有限，必然可能出现一些bug, 所以请大家指出！