The third day of Android training (Java article)

1. Stack memory: Storage of local variables, high efficiency, short life cycle;
   

   Heap Memory: All new objects are stored, the running efficiency is low, the life cycle is long;

   Code area: The object is loaded only when the method is called, and static and non-static methods are generally stored;

   Chang: The stack is shared and can be used to pass values.

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2. Array:

   Concept: A set of elements of the same type with a certain length;

   Classification: one-dimensional, two-dimensional;

   Storage location: heap memory;

   Note: All reference types have their own space in the heap memory.

3. (1) One-dimensional array syntax:

4. 
   

static: int[] a={1,2,3,4}; int a[]=new int[]{1,2,3,4};

Dynamic: int[]b; int b[]=new int[4];

Sort: Bubble Sort method, Comparison method; (22 Compare, use the addition Exchange law to exchange values)

Note: array subscript starting from 0, carefully subscript out of bounds

Array Length: array name. length;

(2) Two-dimensional arrays:

Static: int[][] a={{1},{2,3},{4,5,6}}; Int[][] A=new int[][]{{1},{2,3},{4,5,6}};

Dynamic: int[][] A; Int[][] A=new int[4][]; Int[][] A=new int[3][4];

Note: The length of the two-dimensional array is equivalent to the number of rows, equivalent to the above example int[][] a=new int[4][]; "4" is the length of the two-dimensional array A;

Understand that two-dimensional arrays contain one-dimensional arrays, and that all arrays must have loops in their traversal.

After-school exercises:

1. Use scanner to enter two numbers arbitrarily, greatest common divisor and least common multiple, please use two methods to represent greatest common divisor and least common multiple respectively.

   
   

Code:

Import Java.util.Scanner;

public class A {

public static void Main (string[] args) {

Scanner s = new Scanner (system.in);

System.out.println ("Enter first number:");

int a = S.nextint ();

System.out.println ("Enter a second number:");

int b = S.nextint ();

System.out.println ("Greatest common divisor:" + Gongyueshu (A, b));

SYSTEM.OUT.PRINTLN ("Least common multiple:" + Gongbeishu (A, b));

}

public static int Gongyueshu (int a, int b) {

int in, min = 0;

if (a > B) {

in = B;

} else {

in = A;

}

for (int i = 1; i <= in; i++) {

If (a% i = = 0 && b% i = = 0) {

min = i;

}

}

return min;

}

public static int Gongbeishu (int a, int b) {

int GB = A * B/gongyueshu (a, b);

return GB;

}

}

2.

See the following series, evaluation;

1,2,7,13,49,24,343 ... The sum of the first 20 items;

Code:

public class A {

public static void Main (string[] args) {

int a = 1, b = 2;

int sum = 0, sum1 = 0, sum2 = 0;

for (int i = 1; i <=; i++) {

if (i% 2 = = 0) {

SUM1 = sum + b;

B = B + 11;

} else {

sum2 = sum + A;

A = a * 7;

}

}

sum = sum1 + sum2;

System.out.println ("Top 20 items and:" + sum);

}

}

3. Sort by bubbling:

To sort a given number sequence from small to large:

public class A {

public static void Main (string[] args) {

int a[] = {3, 2, 5, 1, 7};

int b;

for (int i = 0; i < a.length; i++) {

for (int j = 0; J < A.length-1; J + +) {

if (A[j] > a[j + 1]) {

b = a[j + 1];

A[j + 1] = A[j];

A[J] = b;

}

}

}

for (int i = 0; i < a.length; i++) {

System.out.print (A[i] + "");

}

}

}

4. Enter any 3 numbers and output the maximum number

public class A {

public static void Main (string[] args) {

System.out.println ("Please enter 3 integers:");

Scanner s = new Scanner (system.in);

int a = S.nextint ();

int b = S.nextint ();

int c = S.nextint ();

if (a > B) {

if (a > C) {

System.out.println ("The largest number is" + a);

} else {

SYSTEM.OUT.PRINTLN ("Maximum number is" + C);

}

} else {

if (b > C) {

SYSTEM.OUT.PRINTLN ("Maximum number is" + B);

} else {

SYSTEM.OUT.PRINTLN ("Maximum number is" + C);

}

}

}

}

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The third day of Android training (Java article)