Java Learning the next day

One, two common tools

1. Randomly produce a number between [0,1]

math.random ()

Example:

Double box =math.random ();

Generate random decimals [0,1]

System.out.println ("box=" +box);

[Min,max+1]

int min = 5;

int max = 9;

Box =math.random () * (max-min+1) +min;

SYSTEM.OUT.PRINTLN (box);

2, to interact with customers, to obtain the input value of the customer's computer

Java.util.Scanner

Specific steps:

1. Positioning Package: Import Java.util.Scanner

2, Preparation: Scanner tool =new Scanner (system.in)

3, use: Tool.nextint (), tool.nexdouble

Example:

Import Java.util.Scanner;

public class tooldemo02{

public static void Main (string[] args) {

2. Preparation Tools

Scanner tool =new Scanner (system.in);

3. Use

1), get integer

System.out.println ("Please enter Age:");

int age = Tool.nextint ();

System.out.println ("The Age you entered is:" +age);

2), Get decimal

System.out.println ("Please enter elevation:");

Double height =tool.nextdouble ();

System.out.println ("The elevation you entered is:" +height);

　

Second, type conversion

Cause, the data type does not match, in order to match the problem, the type needs to be processed, classified as

Automatic type conversion

Large Type box = small type of data

1, if there is a large number of participation in the operation, the result is a large number of whichever, as far as possible to advance the large number.

2. Within the range of tables: byte short char = literal | constant value

3. When arithmetic:

1), literal | constant value

byte| Short| Char|int =byte Short Char int +byte short char int

2), once a variable is involved in the operation

int =byte short char int +byte short char int

Forcing type conversions

Small Type box = (small type) large type of data;

Note () Scope of action

Example:

/**
Coercion Type conversions: small type variable = (small type) large type of value
Attention point: () Scope of action
*/
public class parsedemo02{
public static void Main (string[] args) {
char ch = ' A ';
int box = CH; Automatic
ch = (char) box; Forced

Double num = 3.5;
box = (int) num; Discard decimal Points
SYSTEM.OUT.PRINTLN (box);

() Scope of action
box = (int) (NUM*2); (int) num*2
SYSTEM.OUT.PRINTLN (box);

generating [0,8] random integers
int max = 8;
int min = 0;
int letter = (int) math.random () * (max-min) +min;
SYSTEM.OUT.PRINTLN (letter);
Correct wording
letter = (int) (Math.random () * (max-min) +min);
SYSTEM.OUT.PRINTLN (letter);

Generate a random lowercase letter capital Letter
97+0--> ' a '
97+1--> ' B '
97+25--> ' Z '
max = ' Z ' +1;
min = 97;
letter = (int) (Math.random () * (max-min) +min);
System.out.println ((char) letter);
' A '

Generate lowercase letters (solve unknown problems based on existing tools)
Char lowerletter = (char) (Math.random () * (' Z '-' a ' + 1) + ' a ');
System.out.println (Lowerletter);
Think about how to generate capital letters

}

}

III. Choice of implementation

Execute at most once

1, if: Conditional boolean value, General interval

"If so," the condition is set up and implemented, divided into three categories

1), Single choice

If (condition) { Execute code block }

Example:

/**
Single choice:
if () {
}

Generates an integer [0,100] that determines whether an even number is the output even
*/
public class ifdemo01{
public static void Main (string[] args) {
1. generating [0,100] integers
int rnd = (int) (Math.random () *101);
System.out.print ("The number produced is:" +rnd);

2. Whether the number is even, if it is even, the output is "even"
Analysis: Even rnd%2==0
/*
Boolean flag = (rnd%2==0);
Apply Selection
if (flag) {
SYSTEM.OUT.PRINTLN ("This number is even");
}
*/

At development time, if the variable is used only once, you can anonymously
if (rnd%2==0) {
SYSTEM.OUT.PRINTLN ("This number is even");
}

}

}

2), Double choice

If (condition) {

Executing code block 1

}else{

Executing code block 2

}

Example:

/**
Dual choice:
if () {
}else{
}
Generates [0,100] integer, determines whether an even number, if the output is an even number, otherwise the output is odd
*/
public class ifdemo02{
public static void Main (string[] args) {
1. generating [0,100] integers
int rnd = (int) (Math.random () *101);
System.out.print ("The number produced is:" +rnd);

2. Whether the number is even, if it is even, the output is "even"
At development time, if the variable is used only once, you can anonymously
if (rnd%2==0) {
SYSTEM.OUT.PRINTLN ("This number is even");
}else{
SYSTEM.OUT.PRINTLN ("This number is odd");

3), Multi-Select

If ( condition 1) {

  // executing code block 1

}else if (condition 2) {

Executing code block 2

}else if (condition 3) {

Executing code block 3

}else{

}

Example

/**
Multiple selection: Enter an integer [1,7] from the keyboard
1. Decide whether it is a weekend or a weekday
*/
Import Java.util.Scanner;
public class ifdemo03{
public static void Main (string[] args) {
Scanner Tools =new Scanner (system.in);

Enter 1-7 integers from the keyboard
int day =tools.nextint ();
if (day==1) {
System.out.println ("Sad reminder weekday");
}else if (day==2) {
System.out.println ("Sad reminder weekday");
}else if (day==3) {
System.out.println ("Sad reminder weekday");
}else if (day==4) {
System.out.println ("Sad reminder weekday");
}else if (day==5) {
System.out.println ("Sad reminder weekday");
}else if (day==6) {
System.out.println ("boring Weekend");
}else if (day==7) {
System.out.println ("boring Weekend");
}
System.out.println ("A Good Life");

if (Day>=1 &&day<=5) {
System.out.println ("Sad reminder weekday");
}else if (day>=6 && day<=7) {
System.out.println ("boring Weekend");
}else{
SYSTEM.OUT.PRINTLN ("wrong input ... ");
}


}

}

2. Switch: Fixed value judgment

Structure

switch (int integer |1.7 string | enum) { Case fixed value 1 (literal | constant): Code 1 Break Case Fixed value 2 (literal | constant): Code 2 Break ...... Default: Other conditions }

Be aware that:

1. Switch fixed value expression

2. Case fixed Value: constant Literal enumeration value

3, default: Generally put in the last, the position is not fixed

4, Break: End switch to prevent the next wear

End: Normal to} encountered break

Example

Import Java.util.Scanner;

public class switchdemo03{

public static void Main (string[] args) {

Scanner tool =new Scanner (system.in);

Receiving month [1,12]

System.out.println ("Please enter the month:");

Int month =tool.nextint ();

Switch (MONTH/3) {

Case 1:

System.out.println ("Chunkun");

Break

Case 2:

System.out.println ("Summer nap");

Break

Case 3:

System.out.println ("Autumn is spent");

Break

Default

System.out.println ("hibernation");

}

The above is a simple form, the following is a complex form.

/*

Switch (month) {

Case 3:

Case 4:

Case 5:

System.out.println ("Chunkun");

Break

Case 6:

Case 7:

Case 8:

System.out.println ("Summer nap");

Break

Case 9:

Case 10:

Case 11:

System.out.println ("Autumn is spent");

Break

Default

System.out.println ("hibernation");

}

*/

}

}

Java Learning next day