Type conversions and examples in Java

1. Automatic conversion type: Small size data type with large capacity of the data type to do the operation, small capacity will be automatically converted to a large data type.

2. Automatic conversion: char,byte,short=>int=>long=>float=>double. The char,byte,short is the int type that is the default between operations.

3. Coercion type conversion; Large capacity conversion to small capacity, to use the coercion type conversion character: (), may result in a loss of precision.

Example: Long l1=121345;

int m1= (int) L1;

SYSTEM.OUT.PRINTLN (ML)

4. The operation between a string (string, plus "") and the base data type can only be a join operation (such as +), and the resulting result is still a string.

Question 1:string str1= "Hello";

Int myint1=12;

Char chr1= ' a ';

System.out.println (STRL+MYINT1+CHR1);//hello12a

System.out.println (MYINT1+CHR1+STR1);//109hello

System.out.println (chrl+strl+myint1);//ahello12

Problem 2:string str1=4;//wrong

String str2=3.5f+ "";//Yes

System.out.println (STR2);//Output 3.5

System.out.println (3+4+ "hello!"); /Output 7hello!

System.out.println ("hello!" +3+4);//Output hello!34

System.out.println (' A ' +1+ "hello!"); /Output 98hello!

System.out.println ("Hello" + ' a ' + 1);//Output HELLOA1

5. Binary: 0 or 1, start with 0b or 0 B, start sign bit, 0 is positive, 1 is negative;

Decimal: 0-9;

Octal: 0-7, beginning with 0;

Hex: 0-9 and A-f, beginning with 0x or 0X, do not differentiate between a-f and casing.

6. Original code, anti-code and complement; ① positive, the original code, anti-code and complement three yards in one; ② negative, the inverse code for the original code on the basis of the symbol bit fixed the rest of the reverse; the complement is +1 on the inverse code.

Question 3:

The value of the problem 4:byte (bottom of the computer-15)

7. Decimal = binary: In addition to 2 the inverse of the remainder

Cases:

8. Binary = octal

9. Binary = Hex

10. Arithmetic operators, + 、-、 *,/,%, + + 、--

11. Division sign;

Title 5:int i=12;

Int J=I/5;

Double D=I/5;

Double d2= (double) i/5;

Double d1=i/5.0;

System.out.println (j);//2

System.out.println (d);//2.0

System.out.println (D2);//2.4

System.out.println (D1); 2.4

12. Modulus,%, remainder, the result of the symbol depends on the modulus

Title 6:int i1=12%5;

Int i2=-12%5;

Int i3=-12% (-5);

Int i4=12% (-5);

System.out.println (i1);//2

System.out.println (I2);//-2

SYSTEM.OUT.PRINTLN (i3);//-2

System.out.println (I4);//2

13. Gaga, minus and minus; + +,--

① before + +: Increment 1 First, then do the operation;

After + +: First do the operation, after the increase of 1;

Title 7:int myint1=10;

Int myint2=myint1++;//after + +

System.out.println (myInt1);//11

System.out.println (MyInt2);//10

Int myint3=10;

Int myint4=++myint;//Pre + +

System.out.println (MYINT3);//11

System.out.println (MYINT4);//11

② before--: first, minus 1, after doing the operation;

After--: first to do the operation, after the reduction of 1;

14. Command-line mode; dir,md,rd,cd,cd..,cd/,del,exit

15.JDK, JRE, and JVM relationships, java program: write = = compile and run.

16. Single-line comments, multiline comments, and document comments, document comments/** */.

Parse Document Comment: javadoc-d file directory name-autor-version source file name. java;

17. Assignment operation; +, + =,-=, *=,/=,%=.

①+=: The operation can be implemented without changing the data type of s;

Title 8:i+=3 equivalent to i=i+3;

Title 9:short s=10;

s=s+3;//compilation does not pass

S= (short) (s+3);//compile through, do not recommend this compilation

s+=3;//can either implement the operation without changing the data type of S

②=: Assignment is not an equal sign;

Title 10:boolean B1=false;

If (b1=true) {System.out.println ("result is true")}

ELSE{SYSTEM.OUT.PRINTLN ("result is false")}

The output is true

Title 11:boolean B1=false;

If (b1==true) {System.out.println ("result is true")}

ELSE{SYSTEM.OUT.PRINTLN ("result is false")}

The output is False

Title 12:int I=1;

i*=0.1;

System.out.println (i);//0, type is still int,0.1 0

18. Comparison operators; ①==, equal to; ②!=,;③<, >, <=, >=;

④instanceof, check whether the object is a class;

Example: "Hello" instanceof string//is True

Type conversions and examples in Java