Java String之StringBuilder以及它的API的详细使用方法
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StringBuilder 简介
StringBuilder 是一个可变的字符序列。它继承于AbstractStringBuilder，实现了CharSequence接口。
StringBuffer 也是继承于AbstractStringBuilder的子类；但是，StringBuilder和StringBuffer不同，前者是非线程安全的，后者是线程安全的。
StringBuilder 和 CharSequence之间的关系图如下：
StringBuilder函数列表
StringBuilder() StringBuilder(int capacity) StringBuilder(CharSequence seq) StringBuilder(String str) StringBuilder append(float f) StringBuilder append(double d) StringBuilder append(boolean b) StringBuilder append(int i) StringBuilder append(long l) StringBuilder append(char c) StringBuilder append(char[] chars) StringBuilder append(char[] str, int offset, int len) StringBuilder append(String str) StringBuilder append(Object obj) StringBuilder append(StringBuffer sb) StringBuilder append(CharSequence csq) StringBuilder append(CharSequence csq, int start, int end) StringBuilder appendCodePoint(int codePoint) int capacity() char charAt(int index) int codePointAt(int index) int codePointBefore(int index) int codePointCount(int start, int end) StringBuilder delete(int start, int end) StringBuilder deleteCharAt(int index) void ensureCapacity(int min) void getChars(int start, int end, char[] dst, int dstStart) int indexOf(String subString, int start) int indexOf(String string) StringBuilder insert(int offset, boolean b) StringBuilder insert(int offset, int i) StringBuilder insert(int offset, long l) StringBuilder insert(int offset, float f) StringBuilder insert(int offset, double d) StringBuilder insert(int offset, char c) StringBuilder insert(int offset, char[] ch) StringBuilder insert(int offset, char[] str, int strOffset, int strLen) StringBuilder insert(int offset, String str) StringBuilder insert(int offset, Object obj) StringBuilder insert(int offset, CharSequence s) StringBuilder insert(int offset, CharSequence s, int start, int end) int lastIndexOf(String string) int lastIndexOf(String subString, int start) int length() int offsetByCodePoints(int index, int codePointOffset) StringBuilder replace(int start, int end, String string) StringBuilder reverse() void setCharAt(int index, char ch) void setLength(int length) CharSequence subSequence(int start, int end) String substring(int start) String substring(int start, int end) String toString() void trimToSize()
AbstractStringBuilder 和 StringBuilder源码
AbstractStringBuilder源码(基于jdk1.7.40)
package java.lang; import sun.misc.FloatingDecimal; import java.util.Arrays; abstract class AbstractStringBuilder implements Appendable, CharSequence { char[] value; int count; AbstractStringBuilder() { } AbstractStringBuilder(int capacity) { value = new char[capacity]; } public int length() { return count; } public int capacity() { return value.length; } public void ensureCapacity(int minimumCapacity) { if (minimumCapacity > 0) ensureCapacityInternal(minimumCapacity); } private void ensureCapacityInternal(int minimumCapacity) { // overflow-conscious code if (minimumCapacity - value.length > 0) expandCapacity(minimumCapacity); } 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); } public void trimToSize() { if (count < value.length) { value = Arrays.copyOf(value, count); } } 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; } } public char charAt(int index) { if ((index < 0) || (index >= count)) throw new StringIndexOutOfBoundsException(index); return value[index]; } public int codePointAt(int index) { if ((index < 0) || (index >= count)) { throw new StringIndexOutOfBoundsException(index); } return Character.codePointAt(value, index); } public int codePointBefore(int index) { int i = index - 1; if ((i < 0) || (i >= count)) { throw new StringIndexOutOfBoundsException(index); } return Character.codePointBefore(value, index); } 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); } 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); } public void setCharAt(int index, char ch) { if ((index < 0) || (index >= count)) throw new StringIndexOutOfBoundsException(index); value[index] = ch; } 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); str.getChars(0, len, value, count); count += len; return this; } // Documentation in subclasses because of synchro difference 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; } // Documentation in subclasses because of synchro difference 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()); } 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; } 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; } public AbstractStringBuilder append(int i) { if (i == Integer.MIN_VALUE) { append("-2147483648"); return this; } int appendedLength = (i < 0) ? Integer.stringSize(-i) + 1 : Integer.stringSize(i); int spaceNeeded = count + appendedLength; ensureCapacityInternal(spaceNeeded); Integer.getChars(i, spaceNeeded, value); count = spaceNeeded; 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 AbstractStringBuilder append(float f) { new FloatingDecimal(f).appendTo(this); return this; } public AbstractStringBuilder append(double d) { new FloatingDecimal(d).appendTo(this); 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) { 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; } 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(); int newCount = count + len - (end - start); ensureCapacityInternal(newCount); System.arraycopy(value, end, value, start + len, count - end); str.getChars(value, start); count = newCount; return this; } 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); } 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); System.arraycopy(value, index, value, index + len, count - index); System.arraycopy(str, offset, value, index, len); count += len; return this; } 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); System.arraycopy(value, offset, value, offset + len, count - offset); str.getChars(value, offset); 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; } public AbstractStringBuilder insert(int offset, boolean b) { return insert(offset, String.valueOf(b)); } 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 AbstractStringBuilder insert(int offset, int i) { return insert(offset, String.valueOf(i)); } public AbstractStringBuilder insert(int offset, long l) { return insert(offset, String.valueOf(l)); } public AbstractStringBuilder insert(int offset, float f) { return insert(offset, String.valueOf(f)); } public AbstractStringBuilder insert(int offset, double d) { return insert(offset, String.valueOf(d)); } 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); } 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); } public AbstractStringBuilder reverse() { boolean hasSurrogate = false; int n = count - 1; 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; } 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; } public abstract String toString(); final char[] getValue() { return value; } } StringBuilder源码(基于jdk1.7.40)
package java.lang; public final class StringBuilder extends AbstractStringBuilder implements java.io.Serializable, CharSequence { static final long serialVersionUID = 4383685877147921099L; // 构造函数。默认的字符数组大小是16。 public StringBuilder() { super(16); } // 构造函数。指定StringBuilder的字符数组大小是capacity。 public StringBuilder(int capacity) { super(capacity); } // 构造函数。指定字符数组大小=str长度+15，且将str的值赋值到当前字符数组中。 public StringBuilder(String str) { super(str.length() + 16); append(str); } // 构造函数。指定字符数组大小=seq长度+15，且将seq的值赋值到当前字符数组中。 public StringBuilder(CharSequence seq) { this(seq.length() + 16); append(seq); } // 追加“对象obj对应的字符串”。String.valueOf(obj)实际上是调用obj.toString() public StringBuilder append(Object obj) { return append(String.valueOf(obj)); } // 追加“str”。 public StringBuilder append(String str) { super.append(str); return this; } // 追加“sb的内容”。 private StringBuilder append(StringBuilder sb) { if (sb == null) return append("null"); int len = sb.length(); int newcount = count + len; if (newcount > value.length) expandCapacity(newcount); sb.getChars(0, len, value, count); count = newcount; return this; } // 追加“sb的内容”。 public StringBuilder append(StringBuffer sb) { super.append(sb); return this; } // 追加“s的内容”。 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()); } // 追加“s从start(包括)到end(不包括)的内容”。 public StringBuilder append(CharSequence s, int start, int end) { super.append(s, start, end); return this; } // 追加“str字符数组对应的字符串” public StringBuilder append(char[] str) { super.append(str); return this; } // 追加“str从offset开始的内容，内容长度是len” public StringBuilder append(char[] str, int offset, int len) { super.append(str, offset, len); return this; } // 追加“b对应的字符串” public StringBuilder append(boolean b) { super.append(b); return this; } // 追加“c” public StringBuilder append(char c) { super.append(c); return this; } // 追加“i” public StringBuilder append(int i) { super.append(i); return this; } // 追加“lng” public StringBuilder append(long lng) { super.append(lng); return this; } // 追加“f” public StringBuilder append(float f) { super.append(f); return this; } // 追加“d” public StringBuilder append(double d) { super.append(d); return this; } // 追加“codePoint” public StringBuilder appendCodePoint(int codePoint) { super.appendCodePoint(codePoint); return this; } // 删除“从start(包括)到end的内容” public StringBuilder delete(int start, int end) { super.delete(start, end); return this; } // 删除“位置index的内容” public StringBuilder deleteCharAt(int index) { super.deleteCharAt(index); return this; } // “用str替换StringBuilder中从start(包括)到end(不包括)的内容” public StringBuilder replace(int start, int end, String str) { super.replace(start, end, str); return this; } // “在StringBuilder的位置index处插入‘str中从offset开始的内容’，插入内容长度是len” public StringBuilder insert(int index, char[] str, int offset, int len) { super.insert(index, str, offset, len); return this; } // “在StringBuilder的位置offset处插入obj对应的字符串” public StringBuilder insert(int offset, Object obj) { return insert(offset, String.valueOf(obj)); } // “在StringBuilder的位置offset处插入str” public StringBuilder insert(int offset, String str) { super.insert(offset, str); return this; } // “在StringBuilder的位置offset处插入str” public StringBuilder insert(int offset, char[] str) { super.insert(offset, str); return this; } // “在StringBuilder的位置dstOffset处插入s” 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()); } // “在StringBuilder的位置dstOffset处插入's中从start到end的内容'” public StringBuilder insert(int dstOffset, CharSequence s, int start, int end) { super.insert(dstOffset, s, start, end); return this; } // “在StringBuilder的位置Offset处插入b” public StringBuilder insert(int offset, boolean b) { super.insert(offset, b); return this; } // “在StringBuilder的位置Offset处插入c” public StringBuilder insert(int offset, char c) { super.insert(offset, c); return this; } // “在StringBuilder的位置Offset处插入i” public StringBuilder insert(int offset, int i) { return insert(offset, String.valueOf(i)); } // “在StringBuilder的位置Offset处插入l” public StringBuilder insert(int offset, long l) { return insert(offset, String.valueOf(l)); } // “在StringBuilder的位置Offset处插入f” public StringBuilder insert(int offset, float f) { return insert(offset, String.valueOf(f)); } // “在StringBuilder的位置Offset处插入d” public StringBuilder insert(int offset, double d) { return insert(offset, String.valueOf(d)); } // 返回“str”在StringBuilder的位置 public int indexOf(String str) { return indexOf(str, 0); } // 从fromIndex开始查找，返回“str”在StringBuilder的位置 public int indexOf(String str, int fromIndex) { return String.indexOf(value, 0, count, str.toCharArray(), 0, str.length(), fromIndex); } // 从后向前查找，返回“str”在StringBuilder的位置 public int lastIndexOf(String str) { return lastIndexOf(str, count); } // 从fromIndex开始，从后向前查找，返回“str”在StringBuilder的位置 public int lastIndexOf(String str, int fromIndex) { return String.lastIndexOf(value, 0, count, str.toCharArray(), 0, str.length(), fromIndex); } // 反转StringBuilder public StringBuilder reverse() { super.reverse(); return this; } public String toString() { // Create a copy, don't share the array return new String(value, 0, count); } // 序列化对应的写入函数 private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException { s.defaultWriteObject(); s.writeInt(count); s.writeObject(value); } // 序列化对应的读取函数 private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { s.defaultReadObject(); count = s.readInt(); value = (char[]) s.readObject(); } } 复制去Google翻译翻译结果
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