JAvaのStringBuilderとStringBufferクラスのソースコードの詳細
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JAvaのStringBuilderとStringBufferクラスのソースコードの詳細
クラスの定義
Javaコンパイラは
文字列は直接つなぎ合わせることができますが、ループでは、ループのたびに新しい文字列オブジェクトが作成され、古い文字列が破棄されます.このように,ほとんどの文字列は一時的なオブジェクトであり,メモリの浪費だけでなくGC効率にも影響を及ぼす.
文字列を効率的につなぎ合わせるために、Java標準ライブラリには
StringBuilderとStringBufferの実現
注意:通常の文字列
クラスの定義
abstract class AbstractStringBuilder implements Appendable, CharSequence {
char[] value;
int count;
AbstractStringBuilder() {
}
AbstractStringBuilder(int capacity) {
value = new char[capacity];
}
@Override
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) {
value = Arrays.copyOf(value,
newCapacity(minimumCapacity));
}
}
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
private int newCapacity(int minCapacity) {
// overflow-conscious code
int newCapacity = (value.length << 1) + 2;
if (newCapacity - minCapacity < 0) {
newCapacity = minCapacity;
}
return (newCapacity <= 0 || MAX_ARRAY_SIZE - newCapacity < 0)
? hugeCapacity(minCapacity)
: newCapacity;
}
private int hugeCapacity(int minCapacity) {
if (Integer.MAX_VALUE - minCapacity < 0) { // overflow
throw new OutOfMemoryError();
}
return (minCapacity > MAX_ARRAY_SIZE)
? minCapacity : MAX_ARRAY_SIZE;
}
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) {
Arrays.fill(value, count, newLength, '\0');
}
count = newLength;
}
}Javaコンパイラは
Stringに対して特殊な処理を行い、+で文字列を直接つなぐことができます.文字列は直接つなぎ合わせることができますが、ループでは、ループのたびに新しい文字列オブジェクトが作成され、古い文字列が破棄されます.このように,ほとんどの文字列は一時的なオブジェクトであり,メモリの浪費だけでなくGC効率にも影響を及ぼす.
文字列を効率的につなぎ合わせるために、Java標準ライブラリには
StringBuilderが用意されています.これは可変オブジェクトであり、バッファを事前に割り当てることができます.これにより、StringBuilderに文字を追加した場合、新しい一時オブジェクトは作成されません.StringBuilder sb = new StringBuilder(1024);
for (int i = 0; i < 1000; i++) {
sb.append(',');
sb.append(i);
}
String s = sb.toString();StringBuilderはまた、チェーン操作を行うことができる.public class Main {
public static void main(String[] args) {
var sb = new StringBuilder(1024);
sb.append("Mr ")
.append("Bob")
.append("!")
.insert(0, "Hello, ");
System.out.println(sb.toString());
}
} public AbstractStringBuilder append(Object obj) {
return append(String.valueOf(obj));
}
public AbstractStringBuilder append(String str) {
if (str == null)
return appendNull();
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 appendNull();
int len = sb.length();
ensureCapacityInternal(count + len);
sb.getChars(0, len, value, count);
count += len;
return this;
}
/**
* @since 1.8
*/
AbstractStringBuilder append(AbstractStringBuilder asb) {
if (asb == null)
return appendNull();
int len = asb.length();
ensureCapacityInternal(count + len);
asb.getChars(0, len, value, count);
count += len;
return this;
}
// Documentation in subclasses because of synchro difference
@Override
public AbstractStringBuilder append(CharSequence s) {
if (s == null)
return appendNull();
if (s instanceof String)
return this.append((String)s);
if (s instanceof AbstractStringBuilder)
return this.append((AbstractStringBuilder)s);
return this.append(s, 0, s.length());
}
private AbstractStringBuilder appendNull() {
int c = count;
ensureCapacityInternal(c + 4);
final char[] value = this.value;
value[c++] = 'n';
value[c++] = 'u';
value[c++] = 'l';
value[c++] = 'l';
count = c;
return this;
}
@Override
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;
}
@Override
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) {
FloatingDecimal.appendTo(f,this);
return this;
}
public AbstractStringBuilder append(double d) {
FloatingDecimal.appendTo(d,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 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> 1; j >= 0; j--) {
int k = n - j;
char cj = value[j];
char ck = value[k];
value[j] = ck;
value[k] = cj;
if (Character.isSurrogate(cj) ||
Character.isSurrogate(ck)) {
hasSurrogates = true;
}
}
if (hasSurrogates) {
reverseAllValidSurrogatePairs();
}
return this;
}
/** Outlined helper method for reverse() */
private void reverseAllValidSurrogatePairs() {
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;
}
}
}
}
@Override
public abstract String toString();
/**
* Needed by {@code String} for the contentEquals method.
*/
final char[] getValue() {
return value;
} StringBuilderとStringBufferの実現
public final class StringBuilder
extends AbstractStringBuilder
implements java.io.Serializable, CharSequence
{
/** use serialVersionUID for interoperability */
static final long serialVersionUID = 4383685877147921099L;
public StringBuilder() {
super(16);
}
public StringBuilder(int capacity) {
super(capacity);
}
/**
* Constructs a string builder initialized to the contents of the
* specified string. The initial capacity of the string builder is
* {@code 16} plus the length of the string argument.
*
* @param str the initial contents of the buffer.
*/
public StringBuilder(String str) {
super(str.length() + 16);
append(str);
}
public StringBuilder(CharSequence seq) {
this(seq.length() + 16);
append(seq);
}
@Override
public StringBuilder append(Object obj) {
return append(String.valueOf(obj));
}
@Override
public StringBuilder append(String str) {
super.append(str);
return this;
}
public StringBuilder append(StringBuffer sb) {
super.append(sb);
return this;
}
@Override
public StringBuilder append(CharSequence s) {
super.append(s);
return this;
}
/**
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder append(CharSequence s, int start, int end) {
super.append(s, start, end);
return this;
}
@Override
public StringBuilder append(char[] str) {
super.append(str);
return this;
}
/**
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder append(char[] str, int offset, int len) {
super.append(str, offset, len);
return this;
}
@Override
public StringBuilder append(boolean b) {
super.append(b);
return this;
}
@Override
public StringBuilder append(char c) {
super.append(c);
return this;
}
@Override
public StringBuilder append(int i) {
super.append(i);
return this;
}
@Override
public StringBuilder append(long lng) {
super.append(lng);
return this;
}
@Override
public StringBuilder append(float f) {
super.append(f);
return this;
}
@Override
public StringBuilder append(double d) {
super.append(d);
return this;
}
/**
* @since 1.5
*/
@Override
public StringBuilder appendCodePoint(int codePoint) {
super.appendCodePoint(codePoint);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder delete(int start, int end) {
super.delete(start, end);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder deleteCharAt(int index) {
super.deleteCharAt(index);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder replace(int start, int end, String str) {
super.replace(start, end, str);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int index, char[] str, int offset,
int len)
{
super.insert(index, str, offset, len);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int offset, Object obj) {
super.insert(offset, obj);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int offset, String str) {
super.insert(offset, str);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int offset, char[] str) {
super.insert(offset, str);
return this;
}
/**
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int dstOffset, CharSequence s) {
super.insert(dstOffset, s);
return this;
}
/**
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int dstOffset, CharSequence s,
int start, int end)
{
super.insert(dstOffset, s, start, end);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int offset, boolean b) {
super.insert(offset, b);
return this;
}
/**
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int offset, char c) {
super.insert(offset, c);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int offset, int i) {
super.insert(offset, i);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int offset, long l) {
super.insert(offset, l);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int offset, float f) {
super.insert(offset, f);
return this;
}
/**
* @throws StringIndexOutOfBoundsException {@inheritDoc}
*/
@Override
public StringBuilder insert(int offset, double d) {
super.insert(offset, d);
return this;
}
@Override
public int indexOf(String str) {
return super.indexOf(str);
}
@Override
public int indexOf(String str, int fromIndex) {
return super.indexOf(str, fromIndex);
}
@Override
public int lastIndexOf(String str) {
return super.lastIndexOf(str);
}
@Override
public int lastIndexOf(String str, int fromIndex) {
return super.lastIndexOf(str, fromIndex);
}
@Override
public StringBuilder reverse() {
super.reverse();
return this;
}
@Override
public String toString() {
// Create a copy, don't share the array
return new String(value, 0, count);
}
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
s.defaultWriteObject();
s.writeInt(count);
s.writeObject(value);
}
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
count = s.readInt();
value = (char[]) s.readObject();
}
}public final class StringBuffer
extends AbstractStringBuilder
implements java.io.Serializable, CharSequence
{
private transient char[] toStringCache;
/** use serialVersionUID from JDK 1.0.2 for interoperability */
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);
}
@Override
public synchronized int length() {
return count;
}
@Override
public synchronized int capacity() {
return value.length;
}
@Override
public synchronized void ensureCapacity(int minimumCapacity) {
super.ensureCapacity(minimumCapacity);
}
/**
* @since 1.5
*/
@Override
public synchronized void trimToSize() {
super.trimToSize();
}
@Override
public synchronized void setLength(int newLength) {
toStringCache = null;
super.setLength(newLength);
}
@Override
public synchronized char charAt(int index) {
if ((index < 0) || (index >= count))
throw new StringIndexOutOfBoundsException(index);
return value[index];
}
/**
* @since 1.5
*/
@Override
public synchronized int codePointAt(int index) {
return super.codePointAt(index);
}
/**
* @since 1.5
*/
@Override
public synchronized int codePointBefore(int index) {
return super.codePointBefore(index);
}
/**
* @since 1.5
*/
@Override
public synchronized int codePointCount(int beginIndex, int endIndex) {
return super.codePointCount(beginIndex, endIndex);
}
@Override
public synchronized int offsetByCodePoints(int index, int codePointOffset) {
return super.offsetByCodePoints(index, codePointOffset);
}
@Override
public synchronized void getChars(int srcBegin, int srcEnd, char[] dst,
int dstBegin)
{
super.getChars(srcBegin, srcEnd, dst, dstBegin);
}
@Override
public synchronized void setCharAt(int index, char ch) {
if ((index < 0) || (index >= count))
throw new StringIndexOutOfBoundsException(index);
toStringCache = null;
value[index] = ch;
}
@Override
public synchronized StringBuffer append(Object obj) {
toStringCache = null;
super.append(String.valueOf(obj));
return this;
}
@Override
public synchronized StringBuffer append(String str) {
toStringCache = null;
super.append(str);
return this;
}
public synchronized StringBuffer append(StringBuffer sb) {
toStringCache = null;
super.append(sb);
return this;
}
/**
* @since 1.8
*/
@Override
synchronized StringBuffer append(AbstractStringBuilder asb) {
toStringCache = null;
super.append(asb);
return this;
}
@Override
public synchronized StringBuffer append(CharSequence s) {
toStringCache = null;
super.append(s);
return this;
}
/**
* @throws IndexOutOfBoundsException {@inheritDoc}
* @since 1.5
*/
@Override
public synchronized StringBuffer append(CharSequence s, int start, int end)
{
toStringCache = null;
super.append(s, start, end);
return this;
}
@Override
public synchronized StringBuffer append(char[] str) {
toStringCache = null;
super.append(str);
return this;
}
/**
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
@Override
public synchronized StringBuffer append(char[] str, int offset, int len) {
toStringCache = null;
super.append(str, offset, len);
return this;
}
@Override
public synchronized StringBuffer append(boolean b) {
toStringCache = null;
super.append(b);
return this;
}
@Override
public synchronized StringBuffer append(char c) {
toStringCache = null;
super.append(c);
return this;
}
@Override
public synchronized StringBuffer append(int i) {
toStringCache = null;
super.append(i);
return this;
}
/**
* @since 1.5
*/
@Override
public synchronized StringBuffer appendCodePoint(int codePoint) {
toStringCache = null;
super.appendCodePoint(codePoint);
return this;
}
@Override
public synchronized StringBuffer append(long lng) {
toStringCache = null;
super.append(lng);
return this;
}
@Override
public synchronized StringBuffer append(float f) {
toStringCache = null;
super.append(f);
return this;
}
@Override
public synchronized StringBuffer append(double d) {
toStringCache = null;
super.append(d);
return this;
}
@Override
public synchronized StringBuffer delete(int start, int end) {
toStringCache = null;
super.delete(start, end);
return this;
}
@Override
public synchronized StringBuffer deleteCharAt(int index) {
toStringCache = null;
super.deleteCharAt(index);
return this;
}
@Override
public synchronized StringBuffer replace(int start, int end, String str) {
toStringCache = null;
super.replace(start, end, str);
return this;
}
@Override
public synchronized String substring(int start) {
return substring(start, count);
}
@Override
public synchronized CharSequence subSequence(int start, int end) {
return super.substring(start, end);
}
@Override
public synchronized String substring(int start, int end) {
return super.substring(start, end);
}
@Override
public synchronized StringBuffer insert(int index, char[] str, int offset,
int len)
{
toStringCache = null;
super.insert(index, str, offset, len);
return this;
}
@Override
public synchronized StringBuffer insert(int offset, Object obj) {
toStringCache = null;
super.insert(offset, String.valueOf(obj));
return this;
}
@Override
public synchronized StringBuffer insert(int offset, String str) {
toStringCache = null;
super.insert(offset, str);
return this;
}
@Override
public synchronized StringBuffer insert(int offset, char[] str) {
toStringCache = null;
super.insert(offset, str);
return this;
}
@Override
public StringBuffer insert(int dstOffset, CharSequence s) {
// Note, synchronization achieved via invocations of other StringBuffer methods
// after narrowing of s to specific type
// Ditto for toStringCache clearing
super.insert(dstOffset, s);
return this;
}
@Override
public synchronized StringBuffer insert(int dstOffset, CharSequence s,
int start, int end)
{
toStringCache = null;
super.insert(dstOffset, s, start, end);
return this;
}
@Override
public StringBuffer insert(int offset, boolean b) {
// Note, synchronization achieved via invocation of StringBuffer insert(int, String)
// after conversion of b to String by super class method
// Ditto for toStringCache clearing
super.insert(offset, b);
return this;
}
@Override
public synchronized StringBuffer insert(int offset, char c) {
toStringCache = null;
super.insert(offset, c);
return this;
}
@Override
public StringBuffer insert(int offset, int i) {
// Note, synchronization achieved via invocation of StringBuffer insert(int, String)
// after conversion of i to String by super class method
// Ditto for toStringCache clearing
super.insert(offset, i);
return this;
}
@Override
public StringBuffer insert(int offset, long l) {
// Note, synchronization achieved via invocation of StringBuffer insert(int, String)
// after conversion of l to String by super class method
// Ditto for toStringCache clearing
super.insert(offset, l);
return this;
}
@Override
public StringBuffer insert(int offset, float f) {
// Note, synchronization achieved via invocation of StringBuffer insert(int, String)
// after conversion of f to String by super class method
// Ditto for toStringCache clearing
super.insert(offset, f);
return this;
}
@Override
public StringBuffer insert(int offset, double d) {
// Note, synchronization achieved via invocation of StringBuffer insert(int, String)
// after conversion of d to String by super class method
// Ditto for toStringCache clearing
super.insert(offset, d);
return this;
}
@Override
public int indexOf(String str) {
// Note, synchronization achieved via invocations of other StringBuffer methods
return super.indexOf(str);
}
@Override
public synchronized int indexOf(String str, int fromIndex) {
return super.indexOf(str, fromIndex);
}
@Override
public int lastIndexOf(String str) {
// Note, synchronization achieved via invocations of other StringBuffer methods
return lastIndexOf(str, count);
}
@Override
public synchronized int lastIndexOf(String str, int fromIndex) {
return super.lastIndexOf(str, fromIndex);
}
@Override
public synchronized StringBuffer reverse() {
toStringCache = null;
super.reverse();
return this;
}
@Override
public synchronized String toString() {
if (toStringCache == null) {
toStringCache = Arrays.copyOfRange(value, 0, count);
}
return new String(toStringCache, true);
}
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);
}
}StringBuilderのソースコードを表示すると、チェーン操作を行う鍵は、定義されたappend()メソッドがthisを返し、それによって、独自の他のメソッドを絶えず呼び出すことができることであることがわかります.StringBuilderを模倣し、チェーン操作をサポートするクラスを設計することもできます.たとえば、増加するカウンタは次のようになります.public class Main {
publicer adder = new Adder();
adder.add(3)
static void main(String[] args) {
Add.add(5)
.inc()
.add(10);
System.out.println(adder.value());
}https://gio.ren/w/YoXDbNoq
}
class Adder {
private int sum = 0;
public Adder add(int n) {
sum += n;
return this;
}
public Adder inc() {
sum ++;
return this;
}
public int value() {
return sum;
}
}
注意:通常の文字列
+の操作では、Javaコンパイラがコンパイル時に複数の連続するStringBuilderの操作を+の操作に自動的に符号化するため、StringConcatFactoryに書き換える必要はありません.実行期間中、StringConcatFactoryは、文字列接続操作を配列コピーまたはStringBuilder操作に自動的に最適化します.StringBufferも聞いたことがあるかもしれませんが、これはJavaの初期のStringBuilderのスレッドセキュリティバージョンで、同期によって複数のスレッド操作StringBufferも安全であることを保証していますが、同期は実行速度の低下をもたらします.StringBuilderとStringBufferのインタフェースはまったく同じで、現在はStringBufferを使用する必要はありません.StringBuilderは可変オブジェクトであり、文字列を効率的に接続するために使用される.StringBuilderは、チェーン動作をサポートすることができ、チェーン動作を実現する鍵は、インスタンス自体を返すことである.StringBufferはStringBuilderのスレッドセキュリティバージョンで、現在はあまり使用されていません.