JAVA 基础

 

一，Primitive Data Types and Operations

Variables: datatype variableName

Constants: final datatype CONSTANTNAME = VALUE

 

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Numeric Data Types and Operations
byte	short	int	long	float	double

 

Shorthand Operators
+=	-=	*=	/=	%=	i++	i--	++i	--i

 

Numeric Type conversions	----------------------------------------->
byte	short	int	long	float	double

 

二，Method

Creating a Method:

modifier retrunValueType methodName (list of paraments){ //method body; }

 

 

 三，Array

 

dataType[] arrayRefVar; dataType arrayRefVar[];

 

dataType[] arrayRefVar = new dataType[arraySize]; dataType arrayRefVar[] = new dataType[arraySize];

 

 

 

三，String and Text I/0

 

Constructing String	String a = new String(“hello”);
String Comparisons	if (string1.equals (stirng2))  or  s1.compareTo(s2)
String Concatenation	s3 = s1.concat(s2)   or  s3 = s1 + s2
Obtaining Substrings	substring(beginIndex, endIndex); substring(index)
String Conversions	toLowerCase, toUpperCase, trim, replace(‘e’,’A’)
Finding a Character/subSting	indexOf
Conversion Array/String	toCharArray(), valueOf(xxx);

 

四，Inheritance and polymorphism

Using the super Keyword: The keyword super  refers to the superclass of the class in which super appears, it can be used in two ways:

1.         To call a superclass constructor

2.         To call a superclass method

 

Casting Objects and the instanceof Operator

 

The final Classes, Methods and Variables

The equals Method

The hashCode Method

The finalize Method

The clone Method

 

五，Abstract Classes and Interfaces

	Variables	Constructors	Methods
Abstract class	No retrictions	Constructors are invoked by subclasses through constructor chaining,An abstract class cannot be instantiated using the new operator.	No restrictions
Interface	All variables must public static finel	No constructors.	All methods must be public abstract instance methods