//: reusing/SprinkSystem.java

// Compostion for code reuse.

class WaterSource{

private String s;

WaterSource() {

System.out.println("WaterSource()");

s = "Constructed";

}

public String toString(){

return s;

}

}

public class SprinklerSystem {

public 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 + " " +

"valve3 = " + valve4 + "\n"+

"i = " + i + " " + "f = " + f + " " +

"source = " + source; // 编译器只能将一个String对象和另一个String对象相加

}

public static void main(String[] args){

SprinklerSystem sprinklers = new SprinklerSystem();

System.out.println(sprinklers);// 每一个非基本类型的对象都有一个toString() 方法，

} // 而且当编译器需要一个String而你只有一个对象时，

// 该方法就会被调用

}