令狐葱@关注互联网

class不为每个reference产生缺省对象，但是对基本数据类型则默认初始化为0

//: c06:SprinklerSystem.java// From 'Thinking in Java, 2nd ed.' by Bruce Eckel// www.BruceEckel.com. See copyright notice in CopyRight.txt.// Composition for code reuse.class WaterSource { private String s; WaterSource() { System.out.println("WaterSource()"); s = new String("Constructed"); } public String toString() { return s; }}public class SprinklerSystem { private String valve1, valve2, valve3, valve4; WaterSource source; int i; float f; void print() { System.out.println("valve1 = " + valve1); System.out.println("valve2 = " + valve2); System.out.println("valve3 = " + valve3); System.out.println("valve4 = " + valve4); System.out.println("i = " + i); System.out.println("f = " + f); System.out.println("source = " + source); } public static void main(String[] args) { SprinklerSystem x = new SprinklerSystem(); x.print(); }} ///:~

输出结果为：

---------- java ----------
valve1 = null
valve2 = null
valve3 = null
valve4 = null
i = 0
f = 0.0
source = null

输出完成 (耗时 0 秒) - 正常终止

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