Details One: string, switch, default value, array

1. Enter a string s to determine if the string str is equal, using: variable. Equals (variable)

2, A. Equals (b), string type comparison is equal
If A is null, an error will be nullpointerexception
Workaround: Put the determination not to be null in front

3, take Max to Min random number, (Math.random () * (max-min+1) +min)

4. Switch (num) {
Case 1:
System.out.println ("123");
Break
Case 2:
System.out.println ("456");
Break
}
When Num=1, if Case 1 does not break, it will perform a down-penetrating final output: 123
456
5, array of array of type char default value is: Empty (show is a space)
Array entries for integer and floating-point arrays The default value is: 0
Array item default value for array of type string: null
Array item of the array of type Boolean default value is: false

6, String a = "Java";
String B = "Length";
A.compareto (b);
CompareTo compares the order of two strings in the order of their mother, returning the result int type
Compare the first letter with the first letter of B as the x-axis 0 coordinate, the first letter of a J in the first two bits of L, then return-2
If the first letter is the same, the second letter is compared until the last letter is found or compared
Returns 0 if the letters are the same
If string a = "arr";
String B = "Arrs";
A.compareto (b);
The return value is-1

7. Sort the array from small to large
Int[] arr = {5,6,1,9,3,7,21,8,4};
Arrays.sort (arr);
8. Bubble sort
int [] arr = {5,9,3,6,1,7,2,8};
for (int i = 0; i < arr.length-1; i++) {
for (int j = 0; J < Arr.length-1-i; J + +) {
if (Arr[j]>arr[j+1]) {
int a = Arr[j];
ARR[J] = arr[j+1];
ARR[J+1] = A;
}
}
}
9. Exchange Sort
int [] arr = {5,9,3,6,1,7,2,8};
for (int i = 0; i < arr.length-1; i++) {
for (int j = i+1; J < Arr.length; J + +) {
if (Arr[i]>arr[j]) {
int a = Arr[i];
Arr[i] = Arr[j];
ARR[J] = A;
}
}
}
10. Select Sort
int [] arr = {5,9,3,6,1,7,2,8};
for (int i = 0; i < arr.length-1; i++) {
int k = i;
for (int j = k+1; J < Arr.length; J + +) {
if (Arr[j]<arr[k])
K = J;
}
if (i! = k) {
int a = Arr[i];
Arr[i] = arr[k];
Arr[k] = A;
}
}
11, you can consider a two-dimensional array, a point in the Y axis of the x-axis coordinates (INT[Y][X])
Declaring a two-dimensional array
int [] arr = new INT[5][5];
Assign value
Arr[0][0] = 1;
ARR[0][1] = 1;
...
declaring and assigning values
int [] arr = {{1,1,1,1,1},{2,2,2,2,2},{3,3,3,3,3},{4,4,4,4,4},{5,5,5,5,5}};
The first length must be assigned, and the second length can be declared without assigning a value (the length is not fixed)
Statement
int [] arr = new int [3][];
Assignment, you must declare the following length before you can assign a value
Arr[0] = new INT[3];
Traversing a two-dimensional array requires a double loop

Details One: string, switch, default value, array