String 对象是不可修改的,对于被String 重载的'+' 和'+=' 运算符来说,当你用它们来连接两个String 对象的时候,它在底层并不会对于每一次连接均生成一个String 对象,取而代之,在底层会有一个非线程安全的可修改的StringBuilder 对象被构造出来,并且调用其append()方法来生成我们需要拼接的字符串.关于这一点,我们可以随便编写一个字符串拼接语句,然后使用JDK自带的javap 工具,通过javap -c 编译后的类文件名 命令来查看其对应的JVM字节码(相…

If we spoke a different language, we would perceive a somewhat different world. Ludwig Wittgenstein(1889-1951) You manipulate objects with references Although you treat everything as an object, the identifier you manipulate is actually "reference&quo…

Java Provides a number of ways to hold objects: An array associates numerical indexes to objects. It holds objects of a known type so that you don't have to cast the result when you're looking up an object. It can be multidimensional, and it can hold…

///:~容我对这个系列美其名曰"读书笔记",其实shi在练习英文哈:-) Introduction to Objects Object-oriented programming(OOP) is part of this movement toward using the computer as an expressive medium. This chapter will introduce you to the basic concepts of OOP, including an…

8.1 A string is a sequenceA string is a sequence of characters. You can access the characters one at a time with the bracket operator: >>> fruit = 'banana' >>> letter = fruit[1] The second statement selects character number 1 from fruit…

Exception guidelines Use exceptions to: Handle problems at the appropriate level.(Avoid catching exceptions unless you know what to do with them.) Fix the problem and call the method that caused the exception again. Patch things up and continue witho…

The twist |_Method-call binding Connecting a method call to a method body is called binding. When binding is performed before the program is run(by the compiler and linker, if there is one), it's called early binding. You might not hava heard the ter…

Reusing Classes 有两种常用方式实现类的重用,组件(在新类中创建存在类的对象)和继承. Composition syntax Every non-primitive object has a toString() method, and it’s called in special situations when the compiler wants a String but it has an object. Inheritance syntax You’re always do…

Method overloading |_Distinguishing overloaded methods If the methods hava the same name, how can Java know which method you mean? There's a simple rule : Each overloaded method must take a unique list of argument types. |_Overloading with primitives…

Runtime type information(RTTI) allows you to discover and use type information while a program is running. All classes are loaded into the JVM dynamically, upon the first use of a class. This happens when the program makes the first reference to a st…