StringBuffer类

  void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
          将字符从此字符串复制到目标字符数组。

//不能被继承

public final class StringBuffer
    extends AbstractStringBuilder
    implements java.io.Serializable, CharSequence{}

 

StringBuffer类继承AbstractStringBuilder，AbstractStringBuilder中有两个属性：

/**
     * The value is used for character storage.
     */
    char[] value;

    /**
     * The count is the number of characters used.
     */
    int count;

几个重要的方法：

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;
    }

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);
    }