java 中类的组合,Java 类中toString 及类的组合

class WaterSource{

private String s;

WaterSource(){

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

s="Contructed";

}

public String toString(){return s;}

}

public class SprinklerSystem {

private String value1,value2,value3,value4;

private WaterSource source=new WaterSource();

private int i;

private float f;

public String toString(){

return

"value1 = "+value1+" "+

"value2 = "+value2+" "+

"value3 = "+value3+" "+

"value4 = "+value4+"\n "+

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

"source = "+source;

}

public static void main(String[] args){

SprinklerSystem sprinker=new SprinklerSystem();

System.out.println(sprinker);

}

}

/*

* 在上面两个类所定义的方法中，有一个很特殊：toString().每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。

*/

输出：

WaterSource() value1 = null value2 = null value3 = null value4 = null  i = 0 f = 0.0 source = Contructed