备考攻略丨AP计算机A的用书建议和详细考点梳理

点击上方“蓝色字”可订阅哦！

在美国大学中学习，计算机知识是必不可少的，在以后的就业中，计算机应用也非常广，因此在选择AP 科目时，很多中国留学生对计算机科目情有独钟。今天我们来梳理一下计算机A的考点，加油备考吧！

首先来看一下计算机学习和复习的用书建议。

辅导书类：

Barron's AP Computer Science A ★★★★★

巴郎的教材完全覆盖AP考试考点，课后题目较多，难度、题型与考试相近，但知识点讲解不够深入，适合作为复习书和刷题使用。

Princeton AP Computer Science A ★★★★

题目难度偏低，适合初学时使用。和巴郎教材二选一即可。

Course Description ★★★★

不管准备任何AP科目考试说明都是最好的学习资料，适合前期明确考试范围和后期查漏补缺时使用。

5 Steps to a 5 ★★★★

例题部分比 Barron 要少，难度相当。

Think Java How to Think Like a Computer Scientist ★★★

由于AP计算机考试中涉及的Java只是java的子集，所以本书只适合作为参考书使用。

下面是考点梳理，做好笔记哦！

1.Introductory Java Language Features

Package And Classes 类和包

public class FirstProg // file name is FirstProg.java

{

public static type1 method1 (parameter list)

{

<code for method1>

}

public static type2 method2 (parameter list)

{

<code for method 2>

}

......

public static void main (String[] args)

{

<your code>

}

}

All java methods must be contained in a class; all program statement must be placed in a method

The class that contains the main method does not contain many additional methods.

reserved words (Keywords): class, public, static, void, main.

public: the class or method is usable outside of the class

static: methods that will not access any objects of a class. The main method must always be static.

Types And Identifiers 标识符和类型

Identifiers 标识符

Identifier: name for a variable, parameter, constant, user-defined method, user-defined class

cannot begin with a digit

Lowercase: for variables and methods

Uppercase: separate into multiple words e.g getName, findSurfaceArea

a class name starts with a capitol letter

Built-in Types 内置类型

int - 整数

boolean - true or false

double - 小数

Storage of Numbers 数值储存

Integers 整数

binary

Integer.MAX_VALUE == 2^31-1

Integer.MIN_VALUE == - 2^31

Floating-Point Numbers 浮点数

NaN"not a number" - undefined number

float & double

sign * mantissa * 2^exponent

round-off error - when floating-point numbers are converted into binary, most cannot be represented exactly

e.g 0.1*26 ≠ 0.1+0.1......(26 terms)

Hexadecimal Numbers 十六进制数

conversion between hex and binary

5 hex = 0101 bin         F hex = 1111 bin

5F hex = 01011111 bin

Final Variable  Final变量

user-defined constant

keyword final

e.g.   final double TAX_RATE = 0.08;

final variable can be declared without initializing it immediately, but can only be given just once

array bound

final int MAXSTUDENTS = 25;

int [] classList = new Int[MAXSTUDENTS];

Operators 运算符

Arithmetic Operators 算数运算符

+ addition   - subtraction   * multiplication   /devision   %mod(remainder)

Relational Operators 关系运算符

== equal to   != not equal to   > greater than   < less than   >= greater or equal to   <= less than or equal to

Relational Operators can only be used in comparison of primitive types.

User defined types : equals, compareTo  methods

floating-point should not be compared directly using relational operators.

Logical Operators 逻辑运算符

! NOT   && AND   || OR

Short-circuit evaluation

evaluated from left to right

evaluation automatically stops as soon as the value of the entire expression is known

Assignment Operators 赋值运算符

Compound assignment operators :

=      +=      -=      *=      /=      %=

Increment and Decrement Operator 递增递减运算符

++      --

Operator Precedence 运算符的优先级

!, ++ , --                                          right to left

* , / , %                                           left to right

+ , -                                                 left to right

<, >, <=, >=                                    left to right

== , !=                                            left to right

&&

||

=, +=, -+, *=, /=, %=                    right to left

Input/Output 输入输出

Escape sequences 转义字符

newline

"      double quot

backslash

Control Structures 控制结构

Decision-Making Control Structures 条件结构

if...

if...else...

nested if

extended if (if...elseif...)

Iteration 循环结构

for (initialization; termination condition; update statement)

The termination condition is tested at the top of the loop

the update statement is performed at the bottom

loop variable should not have its value changed inside the loop body

the scope of the loop variable can be restricted to the loop body by combining the loop variable declaration with the initialization.

for loop

for (SomeType element : collection)

cannot be used to replace or remove elements

hides the index variable that is used with array

for-each loop

 

while (boolean test)

while loop

2.Classes and Objects

Public, Private, Static 公开，私有，静态

public method

accessible to all client program

private method

can be accessed only by methods of that class

information hiding

all instance variables are private

Static variable (class variable)

keep track on statics for objects of the class

accumulate a total

provide a new identity number for each new object of the class

contains a value that is shared by all instances of the class

memory allocation happens once

usage

Methods 方法

Headers

Constructors

default constructor - no arguments

creates an object of the class

name: always the same as the class

has no return type

several constructors provides different ways of initializing an object

public BankAccount ()

{

myPassword = " ";

myBalance = 0.0;

}

BankAccount b = new BankAccount ();

the constructor with parameters

public BankAccount (String password, double balance)

{

myPassword = password;

myBalance = balance;

}

BankAccount c = new BankAccount (KevinC , 800.00);

Object b and c are object variables that store the addresses of their respective BankAccount objects.

Accessors 访问器

accesses a class object without altering the object.

returns some information about the object

getSomething()

Mutator  存取器

changes the state of an object by modifying at least one of its instance variables.

setSomething()

Static Methods  静态方法

main() method

used to test other classes

all method must be static

class name . method name

object name . method name

instance methods : all methods operate on an individual objects of a class (constructors, accessors, mutators)

static methods (class methods) : methods performs an operation for the entire class

Driver Class

Method Overloading  方法重载

two or more methods in the same class having the same name but different parameter lists

signature : name & parameter types

return type is irrelevant

Scope 范围

the region where the variable or method is visible and can be accessed

within the class all instance variable and methods can be simply accessed by name (not dot operator)

local variable : defined inside a method or statement. scope: the point where it is declared to the end of the block to its declaration occurs.

when a block is excited, the memory of a local variable is automatically recycled.

this Keyword

the instance method is always called for a particular object

implicit parameter - this

References 引用

primitive data types : double, int, boolean

reference data types : all objects

Difference : the way they are stored

primitive : each has its own memory slot

reference : contains the same address

aliasing : having two reference for the same object.

The Null Reference

a uninitialized object variable is called a null reference or null pointer

statement : object == null

object = null // set to null

NullPointerException - invoke an instance method with a null reference

if you fail to initialize a local variable in a method before you use it, you will get a compile time error

if you make the same mistake with an instance variable of a class, the code may run without error

if you don't initialize a reference instance variable in a class - NullPointerException

Method Parameters

formal parameter (dummy) : placeholders for actual parameter

actual parameter (argument) : supplied by a particular method in a client program

Passing Primitive types as parameters

When a memory is called, a new memory slot is allocated for each parameter.

Any changes made to parameters will not affect the values of the arguments in the calling program.

Passing Objects as parameters

the address is copied (not the value)

not possible for a method to make an object replace another one

can change the state of the object

3.Inheritance and polymorphism

Inheritance 继承

Superclass and Subclass  超类和子类

a subclass is bigger than a superclass - it contains more methods and data

Inheritance Hierarchy  继承层次结构

a subclass can itself be a superclass of another class

subclass is-a superclass

is-a is transitive

method overriding - rewrite the method from superclass

partial overriding - part of the method is rewritten

Implementing subclasses  实现子类

keyword : extends

public class Superclass

{

// private instance variables

// other data members

// constructors

// public methods

// private methods

}

public class Subclass extends Superclass

{

// additional private instance variables

// additional data members

// constructors (not inherited!)

// additional public methods

// inherited public methods whose implementation is overridden

// additional private methods

}

Inheriting Instance Methods and Variables  继承实例方法和变量

the subclasses inherit all of the methods and variables of the superclass

instance variables are private and not directly accessible to the methods in the subclasses

classes on the same level in a hierarchy diagram do not inherit anything from each other

method overriding and the super keyword  方法重载和super关键字

include a call to the superclass method

subclass method wants to do what the superclass does, plus something extra

a method in a superclass is overridden in a subclass by defining a method with the same return typer and signature

partial overriding

constructors and super   构造函数和super

Constructors are never inherited!

the new instance variable must be explicitly initialized

if super is used in the implementation of a subclass constructor, it must be used in the first line of the constructor body.

if no constructor is provided in a subclass, the compiler provides the following default constructor

public SubClass()

{

Super();   // calls default constructor of superclass

}

Rules for Subclasses

A subclass can add new private instance variables.

A subclass can add new public, private, or static methods.

A subclass can override inherited methods.

A subclass may not redefine a public method as private.

A subclass may not override static methods of the superclass.

A subclass should define its own constructors.

A subclass cannot directly access the private members of its superclass. It must use accessor or mutator methods.

Declaring Subclass Objects  声明子类对象

Student s = new Student();

Student g = new GradStudent();

Student u = new UnderGrad();

A super class does not inherit from a subclass

Polymorphism 多态

Polymorphism is the mechanism of selecting the appropriate method of a particular object in a class hierarchy.

method calls are always determined by the type of the actual object, not the type of object reference.

the selection of the correct method occurs during the run of the program.

Dynamic Binding (Late Binding) 动态绑定（后期绑定）

overloaded - selected at compile time - static binding, early binding

overridden - selected at runtime - late binding

compiler determine if a method can be called

run-time environment determine how it will be called.

Type Compatibility 类型兼容性

Downcasting 向下转换

downcast - casting a superclass to a subclass type

Student s = new GradStudent( );

GradStudent g = new GradStudent( );

int x = s.getID( ); // compile-time error

int y = g.getID( ); // legal

s is of type Student - Student class odes not have a getID method

can be fixed by casting s to the correct type

int x = ((GradStudent) s ).getID( );

the outer parentheses are necessary

The ClassCastException

a run-time exception thrown to signal an attempt to cast an object to a class of which it is not an instance

Abstract Class  抽象类

a superclass that represents an abstract concept

may contains abstract methods - have no implementation code, just a header

appears as a place holder

If a class contains any abstract methods, it must be declared an abstract class

The abstract Keyword  abstract关键字

public abstract class AbstractClass

{ ... }

public class SubClass extends AbstractClass

{ ... }

if a subclass of an abstract class does not provide implementation code for all the abstract methods, it too becomes an abstract class

public abstract class Subclass extends AbstractClass

{ ... }

An abstract class can have both instance variables and concrete methods

the header is terminated with a semicolon

It is possible for an abstract class to have no abstract methods

An abstract class may or may not have constructors

No instances can be created for an abstract class

Polymorphism works with abstract classes as it does with concrete classes

Interfaces  接口

Interface  接口

a collection of related methods whose headers are provided without implementations

all methods are public and abstract (no need to explicitly include these keywords)

provide a framework of behavior for any class

Defining an interface  定义接口

public interface FlyingObject {

void fly();  // method that simulate the flight of the object boolean isFlying();  // true if the object is in flight, false otherwise

}

The implements Keyword

public class Bird implements FlyingObject

public class mosquito extends Insect implements FlyingObject

The Comparable Interface

public interface Comparable

{

int compareTo (Object obj);

}

 

 

4.Some Standard Classes

The Object Class

The Universal Superclass

every class automatically extends Object

Methods in the Object

Object is NOT an abstract class

expectation : the methods will be overridden in any class where default implementation is not suitable

toString

public String toString()

when you attempt to print an object, the inherited default toString method is invokes

Array objects are unusual in that they do not have toString method

equals

public boolean equals(Object another)

return true if this object and other are the same object (referencing to the same memory slot)

equivalent to the == relation

 

The String Class

String Objects

a sequence of characters

immutable - no methods to change them after they've been constructed

constructing String Objects

can be initialized like a primitive type

String s = "abc"

String s = new String("abc");

it is possible to reassign a string reference

The Concatenation Operator

If one of the operands is a String and the other is a primitive type, then the non-String operand is converted to a String

If neither of the operands is a String object, an error occurs

Comparison of String Objects

overridden inherited from the Object class and overridden to do the correct thing:

equal

if (string1 .equals (string2)) ...

the String class implement Comparable

compares Strings in dictionary order

return true if string1 and string2 are identical strings

compareTo

java is case-sensitive

digits precede capital letters precede lowercase letters

Other String Methods

int length(

return the length of this String

String substring(int startIndex)

return a substring starts with the character at startIndex and extends to the end of the string

the first character is at index zero

StringIndexOutOfBoundsException if startIndex is negative or larger than the length of the string

String substring (int startIndex, int endIndex)

start at startIndex, end at endIndex-1

int indexOf(String str)

return the index of the first occurrence of str

return -1 if str is not the substring

if str is null - NullPointerException

Wrapper Classes

The Integer Class

The Double Class

5.Program Design and Analysis

The Water Fall Model 瀑布模型

Analysis of Specification 程序详细计划书

a written description based on costumer's requirements

Program Design 程序设计

detailed overall plan without Java code

include all objects + data structure + list of tasks

Implementation 程序实现

actual coding (具体接下来有)

Testing and Debugging 调试和测试

upgrading code as circumstances change

write a robust program to avoid bad input

compile-time error - occur during compilation e.g. syntax error

run-time error - occur during execution "throws an exception"

intent/ logic error - fails to carry out the specification of the program

typical values in each part of the domain

end point values

out-of-range values

Test Data 测试数据

Types of Errors (bugs) 错误类型

Robustness 稳健性

Program Maintenance 程序维护

Object-Oriented Program Design 面对对象程序设计

Identifying Classes 确定类

Basic Object

Collection

Controller

Display

Identifying Behaviors 确定行为

find all verbs in the program description

encapsulation 封装 bundling a group of methods and data fields into a class

Think carefully about who should do what

Determining Relationships Between Classes 确定类之间的关系

Inheritance Relationship 继承关系 (is-a)

Composition Relationship 组合关系 (has-a)

UML Diagrams  UML图

实心箭头 has-a

空心箭头 is-a

interface 虚线

Implementing Classes 实现类

start with an over view of the program

collaborators: all other classes needed for one particular class

independent: a class without collaborators

Independent classes are written and tested before being incorporated into the overall project

Bottom-Up development自下而上开发

Top-Down development 自上而下开发

Implementing Methods 实现方法

Procedure Abstraction 过程抽象

avoid repeating code

use helper methods

Information Hiding 信息隐藏

instance variable and helper methods are private

Stub Method 存根方法

stub - a dummy method

Algorithm 算法

Identifying Classes 确定类

use nouns in the description

Relationship Between Classes 确定类之间的关系

Identifying Behaviors 确定行为

Decisions 制定

Program Analysis 程序分析

Program Correctness 程序的正确性

Assertion 验证

Precondition 前提条件

postcondition 后置条件

Efficiency 性能

CPU time (number of machine operations required)

Memory (number and complexity of the variables)

best case, worst case, average case

最后，提醒大家，考前记得多刷几遍题哦！