toString(）方法细节

toString()，每一个非基本类型的对象都有一个toString()方法，当编译器需要一个Sting,而你只有一个对象时，该方法会自动调用。

class WaterSource {
private String s;
WaterSource(){
System.out.println("WaterSource()");
s = "Constructed";
}
public String toString(){return s;}
}
public class FuYong01{
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" +
"1 = " + i + " " + "f = " + f + " " +
"source = " + source;　　//自动调用toSting方法
}
public static void main2(String[] args){
FuYong01 fy = new FuYong01();
System.out.println(fy);　　//就相当于System.out.println(fy.toSting());

}
}

运行结果：
WaterSource()
valve1 = null valve2 = null valve3 = null valve4 = null
1 = 0 f = 0.0 source = Constructed

注意：

域中为基本类型是能够被初始化为0，但是对象引用会被初始化为null；看上边输出结果的红色null，就是因为引用的对象。

每一个类中都重写了一个toSting方法；我还以为同一个文件中只能有一个toSring方法了