1. Java Basics

Three technical architectures for Java:

1, the Java EE: the Development enterprise Environment application, mainly for the Web program development.

2, J2SE: The development of desktop applications, is the basis of the other two.

3, J2ME: The development of electronic consumer products and embedded equipment.

Jdk:java Development Kit, installation-time path do not have Chinese and white space.

Jre:java the operating environment.

Configure environment variables: Let the Java jdk\bin directory of tools, can be run in any directory.

New java_home=% Installation Path%\JAVA\JDK

Add%java_home%\bin in Path again, notice that there is a number on the front;

Javac: Compile, when executing Javac, will start the Java compiler program, compile the. java file with the specified extension, and generate a bytecode file that the JVM can recognize, that is, the class file (Java running program).

Java: Run, start the JVM. Load the class library that is required by the runtime and execute on the class file.

Identifiers: Numbers, letters, underscores, $, cannot start with a number.

Constant: The amount that will not change during the run.

Variable: storage space in memory, used to store constants.

Data type:

Basic data type: byte short int long float double char Boolean

Reference data types: arrays, classes, interfaces

%: modulo (take rest), any number%2 is not 0 is 1, can be used for switching operations.

i++: First use and then minus.

>>>: Unsigned right shift.

^: XOR, different sides are true.

>>: Shift Right, divided by 2

(conditional expression)? Expression 1: Expression 2;

1 Switch (expression) {2      Case value 1: 3     execute the statement; 4      Break ; 5     default : 6     execute the statement; 7      Break ;     8 }

Choose the type of four kinds: byte,short,int, char. The enumeration is added later.

While and for: can be interchanged, if you define a variable to control the number of cycles with for, an infinite loop with while (true).

Break: End loop for the for switch

Continue: End this loop and go to the next loop.

Overloading: In the same class, the function name is the same, the parameter type or parameter list is different, regardless of the return value.

Array: Starting with 0, numbering the elements

int[] arr = new INT[4];

int[] arr = new int[]{1,2,3,4};

Exception: Array out of bounds, null pointer exception.

Direct sort:

  Public Static voidSelectsort (int[] arr) {     for(intx = 0; x < arr.length-1; X + +) {        //Why is the initialization value of y x+1? Because every comparison is marked with an X-angle.element is compared with the next element.          for(inty = x + 1; Y < arr.length; y++) {            if(Arr[x] >Arr[y]) {                inttemp =Arr[x]; ARR[X]=Arr[y]; Arr[y]=temp; }        }    }}

Bubble Sort:

1  Public Static voidBubblesort (int[] arr) {2 3      for(intx = 0; x < arr.length-1; X + +) {4         //-X: Let each participating comparison of the meta minus,-1: Avoid the corner mark out of bounds. 5          for(inty = 0; Y < arr.length-x-1; y++) {6             if(Arr[y] > arr[y + 1]) {7                 inttemp =Arr[y];8Arr[y] = arr[y + 1];9Arr[y + 1] =temp;Ten             } One         } A     } -}

Dichotomy (binary search)

1   Public Static intHalfseach (int[] arr,intkey) {2 3     intmin, Mid, Max;4Min = 0;5max = Arr.length-1;6Mid = (max + min)/2;7 8      while(Arr[mid]! =key) {9         if(Key >Arr[mid])TenMin = mid + 1; One         Else if(Key <Arr[mid]) Amax = Mid-1; -  -         if(Min >max) the             return-1; -  -Mid = (max + min)/2; -     } +     returnmid; -}

Array rollover

 1  public  static  void  reversearray (int  [] arr) { 2  for  (int  start = 0, end = arr.length-1; Start < end; start++, End-- 3  int  temp = Arr[start];  4  Arr[start] = Arr[end];  5  arr[end] = temp;  6  7  }  8 } 

Register, local method area, method area, heap, stack

Heap: Local variables (variables in functions, arguments on functions, variables in statements)

Stacks: Arrays and objects

1. Java Basics