java源码阅读StringBuilder

public final class StringBuilderextends AbstractStringBuilderimplements java.io.Serializable, CharSequence

//存储字符的数组
char[] value;//当前数组中已有字符的计数
int count;

//append String
public StringBuilder append(String str) {super.append(str);return this;}
// 父类AbstractStringBuilder中具体实现
public AbstractStringBuilder append(String str) {if (str &＃61;&＃61; null)return appendNull();int len &＃61; str.length();ensureCapacityInternal(count &＃43; len);str.getChars(0, len, value, count);count &＃43;&＃61; len;return this;}

private void ensureCapacityInternal(int minimumCapacity) {// overflow-conscious codeif (minimumCapacity - value.length > 0) {value &＃61; Arrays.copyOf(value,newCapacity(minimumCapacity)); }}private int newCapacity(int minCapacity) {// overflow-conscious codeint newCapacity &＃61; (value.length <<1) &＃43; 2;if (newCapacity - minCapacity <0) {newCapacity &＃61; minCapacity;}return (newCapacity <&＃61; 0 || MAX_ARRAY_SIZE - newCapacity <0)? hugeCapacity(minCapacity): newCapacity;}private int hugeCapacity(int minCapacity) {if (Integer.MAX_VALUE - minCapacity <0) { // overflowthrow new OutOfMemoryError();}return (minCapacity > MAX_ARRAY_SIZE)? minCapacity : MAX_ARRAY_SIZE;}

//指定开始位置insert String
public StringBuilder insert(int offset, String str) {super.insert(offset, str);return this;}//父类AbstractStringBuilder中具体实现
public AbstractStringBuilder insert(int offset, String str) {if ((offset <0) || (offset > length()))throw new StringIndexOutOfBoundsException(offset);if (str &＃61;&＃61; null)str &＃61; "null";int len &＃61; str.length();ensureCapacityInternal(count &＃43; len);System.arraycopy(value, offset, value, offset &＃43; len, count - offset);str.getChars(value, offset);count &＃43;&＃61; len;return this;}