Java Foundation easy to mix Point

1. Binary conversion from low to High: Byte<short (char) <int<long<float<double

2.java Eight basic data types (in the Stack): integer type Byte,short,int,long,

Floating-point type float,double

Character type Char

Boolean Type Boolean True,false

--------------------------------------------------------

String is a reference type, capitalized (exists in heap)

3. int res = 20;  String str = "result is:"; System.out.println (str+res+20);//The result is: 2020 System.out.println (str+ (res+20));//Result: 40

4. The difference between i=i+1 and i+=1 short i = 1; i = i+1; System.out.println (i);//Error short i = 1; i + = 1; System.out.println (i);//i=2; The first right of I first becomes the integer and 1 Add, then assigns to the left I, but the left I is the short type, the precision cannot be from high to the end self-

Moving, so error The second I always be short type, so the accuracy is unchanged, no error

5.&& and & Difference A&&b A is false, then no longer judge B, directly return False a&b A is false, will also judge B, and finally return False | | and | is similar to a| | b A is true, does not judge B, directly returns True A|b A is true, it will also Judge B, and finally returns true

^ for XOR or that is, a true one false, returns true; same return false

6. Bitwise operator binary number The first bit indicates that symbol 0 is positive 1-bit negative >> right-shift arithmetic positive left complement 0, negative left complement 1 >>> unsigned right Shift right, left full complement 0

7. Computer internal data are binary forms exist in the binary system in the computer there are many ways to exist: The original code: 3:0000 0011 The first bit is the sign bit, 0-bit positive, 1-bit negative anti-code: Positive inverse code and the same as the original code, negative anti-code, retain the first bit sign, the rest of the counter -3:1000 00 11 (original code)-->1111 1100 (anti-code) * Complement: Positive anti-code, the original code and complement are the same, the complement of negative numbers = anti-code +1; -3:1000 0011 (original code)-->1111 1100 (anti-code)-->1111 1101 (complement) The calculation and the internal operation of the binary is the complement

Java Foundation easy to mix Point