【其它话题】求助一段java code小弟目前刚刚上手java, 看到think in java里有这一段code，如下：
//:
reusing/SprinklerSystem.java
//
Composition for code reuse.
class
WaterSource {
private
String s;
WaterSource()
{
System.out.println("WaterSource()");
s =
"Constructed";
}
public
String toString() { return s; }
}
public
class SprinklerSystem {
private
String valve1, valve2, valve3, valve4;
private
WaterSource source = new WaterSource();
private
int i;
private
float f;
public
String toString() {
return
"valve1 = " + valve1 + " " +
"valve2
= " + valve2 + " " +
"valve3
= " + valve3 + " " +
"valve4
= " + valve4 + "\n" +
"i
= " + i + " " + "f = " + f + " " +
"source
= " + source;
}
public
static void main(String[] args) {
SprinklerSystem
sprinklers = new SprinklerSystem();
System.out.println(sprinklers);
}
}
/*
Output:
WaterSource()
valve1
= null valve2 = null valve3 = null valve4 = null
i =
0 f = 0.0 source = Constructed
*///:
实在不懂为什么最后output里的source=Constructed. 特地前�
(more...)
不知道有没解释对
SprinklerSystem类里面定义了soure这一变量
private WaterSource source = new WaterSource();
也就是说source 这个变量属于WaterSource类
然后main程序中System.out.println(sprinklers)会调用
public String toString() {
return
"valve1 = " + valve1 + " " +
"valve2 = " + valve2 + " " +
"valve3 = " + valve3 + " " +
"valve4 = " + valve4 + "\n" +
"i = " + i + " " + "f = " + f + " " +
"source = " + source;
}
这里面"source = " + source;这一句又会调用source这一变量（属于WaterSource类）中的
public String toString() { return s; }
而s的初始值是 Constructed
private WaterSource source = new WaterSource();
也就是说source 这个变量属于WaterSource类
然后main程序中System.out.println(sprinklers)会调用
public String toString() {
return
"valve1 = " + valve1 + " " +
"valve2 = " + valve2 + " " +
"valve3 = " + valve3 + " " +
"valve4 = " + valve4 + "\n" +
"i = " + i + " " + "f = " + f + " " +
"source = " + source;
}
这里面"source = " + source;这一句又会调用source这一变量（属于WaterSource类）中的
public String toString() { return s; }
而s的初始值是 Constructed
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