java读书笔记：练习对象引用传递

java对象引用传递实践，理解对象传递和值传递

package cn.com.github;
class NewObject {
public StringBuffer newString() {
StringBuffer buffer = new StringBuffer();
buffer = PassValue.passvalue();
return buffer;
}
}
class NotNewObject {
public StringBuffer newString() {
StringBuffer buffer = null;
//buffer 指向passvalue 中的buffer对象
buffer = PassValue.passvalue();
//不要上一句，直接写
//buffer.append("hello world");
//eclipse会报警告，因为这是一个引用传递 ，eclipse并没有为buffer开辟内存，也就是说没有对象。
return buffer;
}
}
class PassValue {
public static StringBuffer passvalue() {
StringBuffer buffer = new StringBuffer();
//buffer 指向passvalue 中的buffer对象
//new StringBuffer()成为垃圾收集器回收的对象
buffer.append("hello world");
return buffer;
}
}
class QuoteObject{
public StringBuffer newString() {
StringBuffer buffer = null;
//buffer 指向passvalue 中的buffer对象
buffer = PassValue.passvalue();
StringBuffer buffer2 = null;
//buffer2 指向passvalue 中的buffer对象，复制了一份引用
buffer2 = buffer;
buffer2.append("hi,guys");
return buffer2;
}
}
public class NewOrNotObject {
public static void main(String[] args) {
NewObject newObject = new NewObject();
System.out.println(newObject.newString());
//hello world
NotNewObject notNewObject = new NotNewObject();
System.out.println(notNewObject.newString());
//hello world
QuoteObject object = new QuoteObject();
System.out.println(object.newString());
//hello worldhi guys
//结论：buffer起一个引用传递的作用
}
}