toString

toStirng()方法会返回一个“以文本方式表示”此对象的字符串。结果应是一个简明但易于读懂的信息表达式。建议所有子类都重写此方法

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而你却只有一个对象时,该方法便会被调用

package object;
//: reusing/SprinklerSystem.java
// commposition 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 
                "value1 = " + valve1 + " "+
                "value2 = " + valve2 + " "+
                "value3 = " + valve3 + " "+
                "value4 = " + valve4 + "
"+
                "i = " + i + " " + "f = " + f + " " +
                "source = " + source;   //在这里编译器知道你要将一个String对象("source =")
                                        //同WaterSource相加
    }
        public static void main(String[] args)
        {
            SprinklerSystem sprinklers = new SprinklerSystem();
            System.out.println(sprinklers);//当只有一个对象时会自动调用toString()
        }
}/* output:

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

*///~