Java String之StringBuffer以及它的API的详细使用方法
StringBuffer 是一个线程安全的可变的字符序列。它继承于AbstractStringBuilder，实现了CharSequence接口。
StringBuilder 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。
StringBuffer 和 CharSequence之间的关系图如下：
StringBuffer 函数列表
StringBuffer()
StringBuffer(int capacity)
StringBuffer(String string)
StringBuffer(CharSequence cs)
StringBuffer append(boolean b)
StringBuffer append(int i)
StringBuffer append(long l)
StringBuffer append(float f)
StringBuffer append(double d)
synchronized StringBuffer append(char ch)
synchronized StringBuffer append(char[] chars)
synchronized StringBuffer append(char[] chars, int start, int length)
synchronized StringBuffer append(Object obj)
synchronized StringBuffer append(String string)
synchronized StringBuffer append(StringBuffer sb)
synchronized StringBuffer append(CharSequence s)
synchronized StringBuffer append(CharSequence s, int start, int end)
StringBuffer appendCodePoint(int codePoint)
int capacity()
synchronized char charAt(int index)
synchronized int codePointAt(int index)
synchronized int codePointBefore(int index)
synchronized int codePointCount(int beginIndex, int endIndex)
synchronized StringBuffer delete(int start, int end)
synchronized StringBuffer deleteCharAt(int location)
synchronized void ensureCapacity(int min)
synchronized void getChars(int start, int end, char[] buffer, int idx)
synchronized int indexOf(String subString, int start)
int indexOf(String string)
StringBuffer insert(int index, boolean b)
StringBuffer insert(int index, int i)
StringBuffer insert(int index, long l)
StringBuffer insert(int index, float f)
StringBuffer insert(int index, double d)
synchronized StringBuffer insert(int index, char ch)
synchronized StringBuffer insert(int index, char[] chars)
synchronized StringBuffer insert(int index, char[] chars, int start, int length)
synchronized StringBuffer insert(int index, String string)
StringBuffer insert(int index, Object obj)
synchronized StringBuffer insert(int index, CharSequence s)
synchronized StringBuffer insert(int index, CharSequence s, int start, int end)
int lastIndexOf(String string)
synchronized int lastIndexOf(String subString, int start)
int length()
synchronized int offsetByCodePoints(int index, int codePointOffset)
synchronized StringBuffer replace(int start, int end, String string)
synchronized StringBuffer reverse()
synchronized void setCharAt(int index, char ch)
synchronized void setLength(int length)
synchronized CharSequence subSequence(int start, int end)
synchronized String substring(int start)
synchronized String substring(int start, int end)
synchronized String toString()
synchronized void trimToSize() StringBuffer源码(基于jdk1.7.40)
package java.lang;
public final class StringBuffer
extends AbstractStringBuilder
implements java.io.Serializable, CharSequence
{
static final long serialVersionUID = 3388685877147921107L;
public StringBuffer() {
super(16);
}
public StringBuffer(int capacity) {
super(capacity);
}
public StringBuffer(String str) {
super(str.length() + 16);
append(str);
}
public StringBuffer(CharSequence seq) {
this(seq.length() + 16);
append(seq);
}
public synchronized int length() {
return count;
}
public synchronized int capacity() {
return value.length;
}
public synchronized void ensureCapacity(int minimumCapacity) {
if (minimumCapacity > value.length) {
expandCapacity(minimumCapacity);
}
}
public synchronized void trimToSize() {
super.trimToSize();
}
public synchronized void setLength(int newLength) {
super.setLength(newLength);
}
public synchronized char charAt(int index) {
if ((index < 0) || (index >= count))
throw new StringIndexOutOfBoundsException(index);
return value[index];
}
public synchronized int codePointAt(int index) {
return super.codePointAt(index);
}
public synchronized int codePointBefore(int index) {
return super.codePointBefore(index);
}
public synchronized int codePointCount(int beginIndex, int endIndex) {
return super.codePointCount(beginIndex, endIndex);
}
public synchronized int offsetByCodePoints(int index, int codePointOffset) {
return super.offsetByCodePoints(index, codePointOffset);
}
public synchronized void getChars(int srcBegin, int srcEnd, char[] dst,
int dstBegin)
{
super.getChars(srcBegin, srcEnd, dst, dstBegin);
}
public synchronized void setCharAt(int index, char ch) {
if ((index < 0) || (index >= count))
throw new StringIndexOutOfBoundsException(index);
value[index] = ch;
}
public synchronized StringBuffer append(Object obj) {
super.append(String.valueOf(obj));
return this;
}
public synchronized StringBuffer append(String str) {
super.append(str);
return this;
}
public synchronized StringBuffer append(StringBuffer sb) {
super.append(sb);
return this;
}
public StringBuffer append(CharSequence s) {
// Note, synchronization achieved via other invocations
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 synchronized StringBuffer append(CharSequence s, int start, int end)
{
super.append(s, start, end);
return this;
}
public synchronized StringBuffer append(char[] str) {
super.append(str);
return this;
}
public synchronized StringBuffer append(char[] str, int offset, int len) {
super.append(str, offset, len);
return this;
}
public synchronized StringBuffer append(boolean b) {
super.append(b);
return this;
}
public synchronized StringBuffer append(char c) {
super.append(c);
return this;
}
public synchronized StringBuffer append(int i) {
super.append(i);
return this;
}
public synchronized StringBuffer appendCodePoint(int codePoint) {
super.appendCodePoint(codePoint);
return this;
}
public synchronized StringBuffer append(long lng) {
super.append(lng);
return this;
}
public synchronized StringBuffer append(float f) {
super.append(f);
return this;
}
public synchronized StringBuffer append(double d) {
super.append(d);
return this;
}
public synchronized StringBuffer delete(int start, int end) {
super.delete(start, end);
return this;
}
public synchronized StringBuffer deleteCharAt(int index) {
super.deleteCharAt(index);
return this;
}
public synchronized StringBuffer replace(int start, int end, String str) {
super.replace(start, end, str);
return this;
}
public synchronized String substring(int start) {
return substring(start, count);
}
public synchronized CharSequence subSequence(int start, int end) {
return super.substring(start, end);
}
public synchronized String substring(int start, int end) {
return super.substring(start, end);
}
public synchronized StringBuffer insert(int index, char[] str, int offset,
int len)
{
super.insert(index, str, offset, len);
return this;
}
public synchronized StringBuffer insert(int offset, Object obj) {
super.insert(offset, String.valueOf(obj));
return this;
}
public synchronized StringBuffer insert(int offset, String str) {
super.insert(offset, str);
return this;
}
public synchronized StringBuffer insert(int offset, char[] str) {
super.insert(offset, str);
return this;
}
public StringBuffer insert(int dstOffset, CharSequence s) {
// Note, synchronization achieved via other invocations
if (s == null)
s = "null";
if (s instanceof String)
return this.insert(dstOffset, (String)s);
return this.insert(dstOffset, s, 0, s.length());
}
public synchronized StringBuffer insert(int dstOffset, CharSequence s,
int start, int end)
{
super.insert(dstOffset, s, start, end);
return this;
}
public StringBuffer insert(int offset, boolean b) {
return insert(offset, String.valueOf(b));
}
public synchronized StringBuffer insert(int offset, char c) {
super.insert(offset, c);
return this;
}
public StringBuffer insert(int offset, int i) {
return insert(offset, String.valueOf(i));
}
public StringBuffer insert(int offset, long l) {
return insert(offset, String.valueOf(l));
}
public StringBuffer insert(int offset, float f) {
return insert(offset, String.valueOf(f));
}
public StringBuffer insert(int offset, double d) {
return insert(offset, String.valueOf(d));
}
public int indexOf(String str) {
return indexOf(str, 0);
}
public synchronized int indexOf(String str, int fromIndex) {
return String.indexOf(value, 0, count,
str.toCharArray(), 0, str.length(), fromIndex);
}
public int lastIndexOf(String str) {
// Note, synchronization achieved via other invocations
return lastIndexOf(str, count);
}
public synchronized int lastIndexOf(String str, int fromIndex) {
return String.lastIndexOf(value, 0, count,
str.toCharArray(), 0, str.length(), fromIndex);
}
public synchronized StringBuffer reverse() {
super.reverse();
return this;
}
public synchronized String toString() {
return new String(value, 0, count);
}
private static final java.io.ObjectStreamField[] serialPersistentFields =
{
new java.io.ObjectStreamField("value", char[].class),
new java.io.ObjectStreamField("count", Integer.TYPE),
new java.io.ObjectStreamField("shared", Boolean.TYPE),
};
private synchronized void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
java.io.ObjectOutputStream.PutField fields = s.putFields();
fields.put("value", value);
fields.put("count", count);
fields.put("shared", false);
s.writeFields();
}
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
java.io.ObjectInputStream.GetField fields = s.readFields();
value = (char[])fields.get("value", null);
count = fields.get("count", 0);
}
} StringBuffer 示例
源码如下(StringBufferTest.java):
/**
* StringBuffer 演示程序
*
* @author skywang
*/
import java.util.HashMap;
public class StringBufferTest {
public static void main(String[] args) {
testInsertAPIs() ;
testAppendAPIs() ;
testReplaceAPIs() ;
testDeleteAPIs() ;
testIndexAPIs() ;
testOtherAPIs() ;
}
/**
* StringBuffer 的其它API示例
*/
private static void testOtherAPIs() {
System.out.println("-------------------------------- testOtherAPIs --------------------------------");
StringBuffer sbuilder = new StringBuffer("0123456789");
int cap = sbuilder.capacity();
System.out.printf("cap=%d\n", cap);
char c = sbuilder.charAt(6);
System.out.printf("c=%c\n", c);
char[] carr = new char[4];
sbuilder.getChars(3, 7, carr, 0);
for (int i=0; i运行结果：
-------------------------------- testInsertAPIs -------------------------------
{3=three, 2=two, 1=one}
12345StringBUFFERStringBufferBUILDERStringBuilder12345100
true3.141591.414ABCabcde
-------------------------------- testAppendAPIs -------------------------------
abcdeABC1.4143.14159true
10012345StringBuilderBUILDERStringBufferBUFFERString12345
{3=three, 2=two, 1=one}
字符编码
-------------------------------- testReplaceAPIs ------------------------------
sbuilder=ABCDE3456789
sbuilder=9876543210
sbuilder=M123456789
-------------------------------- testDeleteAPIs -------------------------------
sbuilder=123789
str1=23789
str2=78
str3=78
-------------------------------- testIndexAPIs --------------------------------
sbuilder=abcAbcABCabCaBcAbCaBCabc
sbuilder.indexOf("bc") = 1
sbuilder.indexOf("bc", 5) = 22
sbuilder.lastIndexOf("bc") = 22
sbuilder.lastIndexOf("bc", 4) = 4
-------------------------------- testOtherAPIs --------------------------------
cap=26
c=6
carr[0]=3 carr[1]=4 carr[2]=5 carr[3]=6
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