1.关于基本数据类型和引用数据类型初始化的值:
package com.dbzhang.demo2; public class WaterSource { private String s; public WaterSource() { System.out.println("waterResource()"); s = "Constructed"; } public String toString(){ return s; } }
package com.dbzhang.demo2; 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 sprinklerSystem = new SprinklerSystem(); System.out.println(sprinklerSystem); } }输出结果:
waterResource() value1=null value2=null value3=null value4=null i=0 f=0.0 source = Constructed
汇总:
(1)类中的域如果为基本的数据类型,则初始化为0,如果为对象引用初始化为null,而且用对象引用去调用方法的时候会出现异常。
(2)在System.out.println()中当你传入的对象的时候,需要调用toString()方法转化成string类型;
(3)非基本数据类型都会有一个toString()方法;