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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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.
(1) One-dimensional array syntax:
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:
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)