StringBuildER、StringBuffer

/**
测试StringBuildER、StringBuffer
*/
public class TestStringBuilder {
public static void main(String[] args) {
String str;

//stringbuilder线程不安全，效率高(一般使用它)。stringbuffer线程安全，效率低
StringBuilder sb = new StringBuilder("abcdefg");

System.out.println(Integer.toHexString(sb.hashCode()));
System.out.println(sb);

sb.setCharAt(2, 'M');
System.out.println(Integer.toHexString(sb.hashCode()));
System.out.println(sb); //abMdefg

}
}