It 18 Palm Third day Course summary

It 18 palm Big data third day the meaning     function of the 1.&NBSP;1 function is defined as a separate applet in the class that has a specific function. The     function is also called a method.  1.2 function format     modifier   return value type   function name (parameter type   formal parameter 1, parameter type   form Parameter 2, ...)    {     EXECUTE statement;    return  return value;    }      the data type of the return value is the      parameter that is determined by the result of the function's run: is a variable that stores the actual arguments passed to the function when the function is called       actual parameters: Specific values passed to formal parameters     return: Used to end functions      return values  :  The result of the function's operation, which is returned to the caller.  **     for cases where the function does not have a specific return value, the return value type uses the keyword void to denote,  if the return statement in the function can be omitted from the last line if not written. Note that only functions can be called in the:     function, and functions cannot be defined inside the function.      when a function is defined, the result of the function should be returned to the caller, which is handled by the caller. The    function needs to be clear when applying the function of      define what the final result is      whether unknown content is required to participate in the operation during the process of defining the function explicitly    defines a function that implements two integers added  class FunctionTest {    public static  Void main (String [] args) {        system.out.println (Sum (2,3)); }  public static  Int sum (int a , int b) {               return a+b;  }}      This function can implement overloading of call functions on sum      in the same class, allow more than one function of the same name, as long as their number of arguments or different types of parameters     feature:    is independent of the return value, see only the parameter list     class functiontest {    public static void main ( String [] args) {        system.out.println (Sum (2,3)); System.out.println (Sum (2,3,4));  }  public static int sum (int a ,  INT&NBSP;B) {  //defines two parameters     return a+b;  }  public  Static int sum (int a, int b, int c) {  //defines three parameters that can be     return a+b+c; &nbSP;}} Array  array----------------concept  :  A collection of data of the same type. (An array is a container) benefit:  can automatically number the    elements in the array, starting with 0, to conveniently manipulate these elements. Format:    format 1   element type []  array name  = new  element type  [element number or array length]   example:   int [] arr =new int [6] //represents the length of the  ,  element of the element  int is 6   (Result is 7 elements since 0)    format 2   element type []  array name  = new [] {  element, element ...};    Example:  int [] arr =new int []{1,2,3};  int []  Arr= {3,5,7,9};class arraydemo {public static void main (String[] args)  {int[] arr=new int [6];int[] arr2=new int[]{1,2,3};int [] arr3=  {3,5,7,9}; System.out.println (arr.length);  //  print array length   arr.length is the default property    System.out.println (arr2.length); System.out.println (arr3.length); }}   array in memory form        arrays are contiguous in memory        the following table starts with 0   //access to a number in an array   you can use ARR (subscript   to implement   such as [1,2,3,4]  arr[0]  that represents the first number of the array 1.      //the length of the array is The maximum value in the  arr[length]  array is the number of arr[length-1]        in the array without arr[length], If the interview will be error   //arraindexoutofboundexception : Array out of bounds exception          int[] arr=new int [6];   a total of three steps  1-defines an array of type int 2-Creates a space in memory 3-associates the two together     Heap:heap   ---------------       object heap     //arrays are located in heap        // new instances are in heap memory      //because all objects are in the heap area, if the heap settings are too small, the object will be stacked overflow (usually stack overflow)     heap overflow  heap overflow      stack overflow  stack Overflow    stack  stack  ----------------       &nbspThe;  method stack method stack corresponds to at least one thread (the thread where the main course main function is located) each method in the stack is called   a method frame  method frame push  stack  :  stack pop   stack : Stack     java no pointer refers to an explicit pointer operation. The reference is the pointer (the name of the variable)     NullPointerException  is a null pointer exception (runtimeexception)//arr []=null;    is run-time exception   practice; takes the maximum value in the array and encapsulates the  class  ArrayMax{                          The name of the       //class must be the same as the name of the file after it is compiled, otherwise the run will error. Public static void main (String[] args)  {    system.out.println ( Getmax (new int []{2,5,21,5,7}));}   public static int getMax  (Int [] arr) { //from robustness considerations should take into account the arr== The null and arr.length  lengths are 0.           if  (arr == null| |  arr.length==0) {  //Short circuit andFirst judge the big  system.out.println ("array does not exist");  return -1;   //when in both cases, the error is prompted and a result of 1 is returned.          }        int  temp =integer.min_value;  //integer.min_value is the minimum value of the integer number for  (int i=0; i  < arr.length ; i++ ) {if  (Temp < arr[i]) { temp =  arr[i] ; }}    return temp;  }    } If the minimum value in the array is evaluated , it is necessary to replace the Temp =integer.min_malue with---> temp =integer.max.malue, temp<arr (i)-->temp >arr (i) to sort the array    (from small to large)   thoughts    iterated algebraic group elements--Find the corner mark corresponding to the minimum and minimum values--displacement position--return array--encapsulation--Call class   arrayselectsort{public static void main (String[] args)  {outArr (sort (new  int []{2,1,6,4,9});  //call Array}   public static int[] sort (Int[] arr ) {&NBSP;&NBSP;&NBSP;&NBsp;  if  (arr == null| |  arr.length == 0) {           // Exclusion of null and length of 0  system.out.println ("Array does not exist");   }      // Determine the minimum value of the number in the next digit   for  (int i =0;i < arr.length ;i++ ) { // Iterate through all the numbers in the array    int aa=Integer.MAX_VALUE;       int  index = 0 ;     //the initial variable that defines the angle label is 0           for  (int j= i + 1;j < arr.length;j++ )  {//all numbers following the arr[i] number, to find the minimum value   if  ( aa > arr [j]) {&NBSP;&NBSP;AA  = arr [j]; //assigns a small value to temp   index = j ;  // Gets the small value of the corner label//  system.out.println (AA)  ;  }     } // Select the smaller of the numbers in the backValue, if it is smaller than itself, swap position if  (ARR[I]&GT;AA) {    arr[index] = arr[i];  //   Arr[i] This larger value is assigned to Arr[index], where arr[index] acts as an intermediate amount, at which time arr[] is empty arr[i] =aa ; //then aa  Assigning a value to a arr[i]    that is already a null value implements the interchange position of the two numbers.  }  }    return arr; //return arr  Array   }    public static void outArr  (Int [] arr) {  //Package outarr  method      for  (int i = 0; i < arr.length ;i++  ) {          system.out.print (arr[i]+ " ");   //Print  arr[i] this array      }   }} question: ****************************** Why when                 int aa=Integer.MAX_VALUE;        in:                int index  = 0 ;    in:         for  (int  i =0;i < arr.length ;i++ ) { //The result of printing is incorrect when traversing all the numbers in the array. Bubble Sort * * * bubble sort, the value will be automatically compared with the next one * * * * SO  5,4,3,2,1   If the bubble sort,   only need to fetch &NBSP;ARR[3]  ,arr[3] will be automatically compared with arr[4]. So you don't need to take arr[4] Example: Use a large number of sinks   bubble sort Class  bubblesort{public static void main (String [] args)  {outarr (Bubble (new int[]{ 3,6,8,2,1,5,9}));} public static int[] bubble  (Int [] arr)  {  //definition function Array           //large number of sinking way        for  (int  i = 0;i < arr.length - 1 ;i++ ) {  //Outer loop count   for arr.length-1          for  (int j  = 0;j < arr.length - 1 - i ;j++ ) {       //n Inner Loop frequency is  arr.length-1-i              int temp= 0;  //defines a temporary variable   is used to receive data  //the data is swapped (because it is a large number sinking way)  if ( Arr[j]>arr[j+1]) {             temp =  arr[j];             arr[j]=arr[j+1];  arr[j+1]=temp;}         }}           return arr;  //returns the array   }     public static void  outarr (Int [] arr) {   //encapsulation method   for  (int i=0 ;i< Arr.length&nbSP;; i++ ) {  system.out.print (arr[i]+ " ");  } }}***************         for  (int j = 0;j < arr.length -  2 - i ;j++ ) {      //n inner loop count is  arr.length-1-i why-2   and  -1  results same *************** binary lookup if the search results are 10 1,3 ,5 ,7,8,10,11   binary   The first binary words are 7, the second binary is 10 (second time from 8)   binary find   data to order   Find the first occurrence of  6 in 1-9 numbers.  class  halffind{public static void main (String[] args)  {   System.out.println (Find (new int []{1,2,3,4,5,6,7,8,9},6));}  public static int find (int [] arr,int n) {  //definition function   * definition   A int  type of digital       int a = 0 ;int b =  arr.length ; int m = 0 ;  //define three variables   "A&nbsP;b "Corner Mark  m  (for median value)     int mindex = 0;  //Intermediate angle Mark       //defining Loops      while  (A&NBSP;&LT;=&NBSP;B) {    //Cycle conditions  mindex  =   (a + b)  /2 ; //calculate the midpoint of the intermediate volume                m  = arr[mindex];      //calculate the value of M                              //Judge M and              if  ( m == n ) {   //if m  and query values are equal     note is   "= ="            return mindex;                   }            //query range falls on the left               else if (m > n) {             b= mindex - 1;                  }              //query range falls to the right               else {                a = mindex + 1;                }                }    return - 1 ;     //return value       &nbSP;&NBSP;&NBSP;&NBSP;}&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP: Array of arrays---------------------     Two-dimensional array        format 1:      int [][] arr = The new int [3][4]; //represents a two-dimensional array named arr, with 3 two-dimensional arrays, 4 elements per group           the names of each array are  arr[0],arr[1];arr[2];         If you assign a value of   to the first array with a corner mark of 1, the notation is arr[0][1]= x;        format 2;        int[][] arr= new int[2][];           2 One-dimensional arrays in two-dimensional arrays           each one-dimensional array is the default initialization value null           can initialize this two one-dimensional array individually            arr[0] = new int[3];  //the first array of   has 3 elements.           arr[1] = new int[1];   //  the second array of    has 1 elements.   Print inverted two-dimensional array class multiarray {public static void main (String[] args)  { int [][] arr= new int[4][3];  //defines a two-dimensional array arr[4][3]int a= 12; // Defines a number starting from 12 for  (int i = 0;i<arr.length ;i++ ) {   //defines the outer function   (with several two-dimensional arrays)             for  (int j  = 0;j<3 ;j++ ) {  //defines the inner layer function (how many elements are in each array) arr [i][j] = a;   //assignment of a--;  //to the first J element of line I 1               }}outarr (arr);    //call}public static void outarr (int [][]  arr) { //definition outarr  function      for  (int i = 0;i  <arr.length ;i++ ) {               for  (int j=0 ;j< 3 ;j++  ) { system.out.print (arr[i][j]+ "\ T"),  //print Arr[i][j] Value               }                 system.out.println ();     }}}/*123      [0][0]  [0][1]  [0][2]  456             [1][0]  [1][1]  [1][2]  789      [2][0]  [2][1]  [2][2]  101112            [3][0]  [3][1]  [3][2]121110        [3][2]  [3][1]  [3][0]      [i][j]        arr.length-1-i987        [2][2]  [2][1]  [2][0]  &NBSP;&NBSP;&NBSP;&NBSP;&NBSP;A--654&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;&NBSP;[1][2]&NBSP;&NBSP;[1][1]   [1][0]321        [0][2]  [0][1]  [0][0 ]*/

It 18 Palm Third day Course summary