StringBuffer和StringBuilder的区别

StringBuffer

 * A thread-safe, mutable sequence of characters.
 * A string buffer is like a {@link String}, but can be modified. At any
 * point in time it contains some particular sequence of characters, but
 * the length and content of the sequence can be changed through certain
 * method calls.

　　StringBuffer是线程安全的，可变字符序列。

　　StringBuffer像String,但是可以被修改。

 

常用的方法：

1.length():返回字符串的数量。

 public int length() {
        return count;
    }

2.StringBuffer构造函数　

初始化函数，StringBuffer的容量是初始的参数的长度+16.

/**
     * Constructs a string buffer initialized to the contents of the
     * specified string. The initial capacity of the string buffer is
     * {@code 16} plus the length of the string argument.
     *
     * @param   str   the initial contents of the buffer.
     */
    @HotSpotIntrinsicCandidate
    public StringBuffer(String str) {
        super(str.length() + 16);
        append(str);
    }

3.根据索引得到字符

    /**
     * @throws IndexOutOfBoundsException {@inheritDoc}
     * @see        #length()
     */
    @Override
    public synchronized char charAt(int index) {
        return super.charAt(index);
    }

 如何使用：如下

 StringBuffer sb = new StringBuffer("ABCEDFG");
 System.out.println(sb.charAt(1));