StringBuffer 详解 (String系列之3)

本章介绍StringBuffer以及它的API的详细使用方法。

转载请注明出处：http://www.cnblogs.com/skywang12345/p/string03.html

StringBuffer 简介

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<carr.length; i++)
            System.out.printf("carr[%d]=%c ", i, carr[i]);
        System.out.println();

        System.out.println();
    }

    /**
     * StringBuffer 中index相关API演示
     */
    private static void testIndexAPIs() {
        System.out.println("-------------------------------- testIndexAPIs --------------------------------");

        StringBuffer sbuilder = new StringBuffer("abcAbcABCabCaBcAbCaBCabc");
        System.out.printf("sbuilder=%s\n", sbuilder);

        // 1. 从前往后，找出"bc"第一次出现的位置
        System.out.printf("%-30s = %d\n", "sbuilder.indexOf(\"bc\")", sbuilder.indexOf("bc"));

        // 2. 从位置5开始，从前往后，找出"bc"第一次出现的位置
        System.out.printf("%-30s = %d\n", "sbuilder.indexOf(\"bc\", 5)", sbuilder.indexOf("bc", 5));

        // 3. 从后往前，找出"bc"第一次出现的位置
        System.out.printf("%-30s = %d\n", "sbuilder.lastIndexOf(\"bc\")", sbuilder.lastIndexOf("bc"));

        // 4. 从位置4开始，从后往前，找出"bc"第一次出现的位置
        System.out.printf("%-30s = %d\n", "sbuilder.lastIndexOf(\"bc\", 4)", sbuilder.lastIndexOf("bc", 4));

        System.out.println();
    }

    /**
     * StringBuffer 的replace()示例
     */
    private static void testReplaceAPIs() {

        System.out.println("-------------------------------- testReplaceAPIs ------------------------------");

        StringBuffer sbuilder;

        sbuilder = new StringBuffer("0123456789");
        sbuilder.replace(0, 3, "ABCDE");
        System.out.printf("sbuilder=%s\n", sbuilder);

        sbuilder = new StringBuffer("0123456789");
        sbuilder.reverse();
        System.out.printf("sbuilder=%s\n", sbuilder);

        sbuilder = new StringBuffer("0123456789");
        sbuilder.setCharAt(0, 'M');
        System.out.printf("sbuilder=%s\n", sbuilder);

        System.out.println();
    }

    /**
     * StringBuffer 的delete()示例
     */
    private static void testDeleteAPIs() {

        System.out.println("-------------------------------- testDeleteAPIs -------------------------------");

        StringBuffer sbuilder = new StringBuffer("0123456789");

        // 删除位置0的字符，剩余字符是“123456789”。
        sbuilder.deleteCharAt(0);
        // 删除位置3(包括)到位置6(不包括)之间的字符，剩余字符是“123789”。
        sbuilder.delete(3,6);

        // 获取sb中从位置1开始的字符串
        String str1 = sbuilder.substring(1);
        // 获取sb中从位置3(包括)到位置5(不包括)之间的字符串
        String str2 = sbuilder.substring(3, 5);
        // 获取sb中从位置3(包括)到位置5(不包括)之间的字符串，获取的对象是CharSequence对象，此处转型为String
        String str3 = (String)sbuilder.subSequence(3, 5);

        System.out.printf("sbuilder=%s\nstr1=%s\nstr2=%s\nstr3=%s\n",
                sbuilder, str1, str2, str3);

        System.out.println();
    }

    /**
     * StringBuffer 的insert()示例
     */
    private static void testInsertAPIs() {

        System.out.println("-------------------------------- testInsertAPIs -------------------------------");

        StringBuffer sbuilder = new StringBuffer();

        // 在位置0处插入字符数组
        sbuilder.insert(0, new char[]{'a','b','c','d','e'});
        // 在位置0处插入字符数组。0表示字符数组起始位置，3表示长度
        sbuilder.insert(0, new char[]{'A','B','C','D','E'}, 0, 3);
        // 在位置0处插入float
        sbuilder.insert(0, 1.414f);
        // 在位置0处插入double
        sbuilder.insert(0, 3.14159d);
        // 在位置0处插入boolean
        sbuilder.insert(0, true);
        // 在位置0处插入char
        sbuilder.insert(0, '\n');
        // 在位置0处插入int
        sbuilder.insert(0, 100);
        // 在位置0处插入long
        sbuilder.insert(0, 12345L);
        // 在位置0处插入StringBuilder对象
        sbuilder.insert(0, new StringBuffer("StringBuilder"));
        // 在位置0处插入StringBuilder对象。6表示被在位置0处插入对象的起始位置(包括)，13是结束位置(不包括)
        sbuilder.insert(0, new StringBuffer("STRINGBUILDER"), 6, 13);
        // 在位置0处插入StringBuffer对象。
        sbuilder.insert(0, new StringBuffer("StringBuffer"));
        // 在位置0处插入StringBuffer对象。6表示被在位置0处插入对象的起始位置(包括)，12是结束位置(不包括)
        sbuilder.insert(0, new StringBuffer("STRINGBUFFER"), 6, 12);
        // 在位置0处插入String对象。
        sbuilder.insert(0, "String");
        // 在位置0处插入String对象。1表示被在位置0处插入对象的起始位置(包括)，6是结束位置(不包括)
        sbuilder.insert(0, "0123456789", 1, 6);
        sbuilder.insert(0, '\n');

        // 在位置0处插入Object对象。此处以HashMap为例
        HashMap map = new HashMap();
        map.put("1", "one");
        map.put("2", "two");
        map.put("3", "three");
        sbuilder.insert(0, map);

        System.out.printf("%s\n\n", sbuilder);
    }

    /**
     * StringBuffer 的append()示例
     */
    private static void testAppendAPIs() {

        System.out.println("-------------------------------- testAppendAPIs -------------------------------");

        StringBuffer sbuilder = new StringBuffer();

        // 追加字符数组
        sbuilder.append(new char[]{'a','b','c','d','e'});
        // 追加字符数组。0表示字符数组起始位置，3表示长度
        sbuilder.append(new char[]{'A','B','C','D','E'}, 0, 3);
        // 追加float
        sbuilder.append(1.414f);
        // 追加double
        sbuilder.append(3.14159d);
        // 追加boolean
        sbuilder.append(true);
        // 追加char
        sbuilder.append('\n');
        // 追加int
        sbuilder.append(100);
        // 追加long
        sbuilder.append(12345L);
        // 追加StringBuilder对象
        sbuilder.append(new StringBuffer("StringBuilder"));
        // 追加StringBuilder对象。6表示被追加对象的起始位置(包括)，13是结束位置(不包括)
        sbuilder.append(new StringBuffer("STRINGBUILDER"), 6, 13);
        // 追加StringBuffer对象。
        sbuilder.append(new StringBuffer("StringBuffer"));
        // 追加StringBuffer对象。6表示被追加对象的起始位置(包括)，12是结束位置(不包括)
        sbuilder.append(new StringBuffer("STRINGBUFFER"), 6, 12);
        // 追加String对象。
        sbuilder.append("String");
        // 追加String对象。1表示被追加对象的起始位置(包括)，6是结束位置(不包括)
        sbuilder.append("0123456789", 1, 6);
        sbuilder.append('\n');

        // 追加Object对象。此处以HashMap为例
        HashMap map = new HashMap();
        map.put("1", "one");
        map.put("2", "two");
        map.put("3", "three");
        sbuilder.append(map);
        sbuilder.append('\n');

        // 追加unicode编码
        sbuilder.appendCodePoint(0x5b57);    // 0x5b57是“字”的unicode编码
        sbuilder.appendCodePoint(0x7b26);    // 0x7b26是“符”的unicode编码
        sbuilder.appendCodePoint(0x7f16);    // 0x7f16是“编”的unicode编码
        sbuilder.appendCodePoint(0x7801);    // 0x7801是“码”的unicode编码

        System.out.printf("%s\n\n", sbuilder);
    }
}

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