字节数组转成指定编码的字符串的问题

import java.io.UnsupportedEncodingException;

public class Test {

/**
* @param args
* @throws UnsupportedEncodingException
*/
public static void main(String[] args) throws UnsupportedEncodingException {
// TODO Auto-generated method stub
byte[] byteArray = new byte[] {12,-69,63,-126,-1};
int length = 0;
length = byteArray.length;
for (int i = 0; i < length; i++) {
System.out.println("byteArray[" + i + "]=" + byteArray[i]);
}
length = byteArray.length;
String str = new String(byteArray, "UTF-8");
System.out.println("str=" + str);
byte b[] = str.getBytes("UTF-8");
int len = b.length;
for (int i = 0; i < len; i++) {
System.out.println("b[" + i + "]=" + b[i]);
}
}
}

输出结果
byteArray[0]=12
byteArray[1]=-69
byteArray[2]=63
byteArray[3]=-126
byteArray[4]=-1
str=�?��
b[0]=12
b[1]=-17
b[2]=-65
b[3]=-67
b[4]=63
b[5]=-17
b[6]=-65
b[7]=-67
b[8]=-17
b[9]=-65
b[10]=-67

为什么字节数组不能还原了