Think in java 答案_Chapter 4_Exercise 16

阅前声明: http://blog.csdn.net/heimaoxiaozi/archive/2007/01/19/1487884.aspx

/****************** Exercise 16 *****************
* Create a class with a String field that is
* initialized at the point of definition, and
* another one that is initialized by the
* constructor. What is the difference between
* the two approaches?
***********************************************/
public class E16_StringInitialization {
  String s1 = "Initialized at definition";
  String s2;
  public E16_StringInitialization(String s2i) {
    s2 = s2i;
  }
  public static void main(String args[]) {
    E16_StringInitialization si =
      new E16_StringInitialization(
        "Initialized at construction");
    System.out.println("si.s1 = " + si.s1);
    System.out.println("si.s2 = " + si.s2);
  }
}

//+M java E16_StringInitialization

**The s1 field is initialized before the constructor is entered. Technically, so is the s2 field, as it is set to null as the object is created. The s2 field has flexibility, since you can choose what value to give it as you call the constructor, whereas s1 will always have the same value.