Java Learning Notes (ii)----BASIC data type Application

& and && and difference,&& if the equation is not set up on the short circuit, and no matter the left of the formation, the right equation is executed
&& short circuit with, | | Short Circuit or
| Or, both sides of the expression are operating regardless of the result

Float f=3.5 wrong, because 3.5 is double type
Float f=3.5f to
All of the byte, short, and char values are promoted to int in an expression

Note: In an expression, whichever is the highest type of variable or number, its next variable or value is converted to the type of the variable or value

BYTE A=1;
a=a+1; Wrong because the result of A+1 has been converted to int, so a can't receive int type
System.out.println (' a ' + 1); The output is 98, because the ' a ' is automatically promoted to integral type.
System.out.println ("" + ' a ' + 1); The output is A1 because in an expression, if a string is added with the + number and other data types, the string is actually concatenated with the other content to generate a new string.

int x=5,y;
Y=x%-2; Y=1
y=-x%2//Y=-1

Switch
The selector in the switch must be an int or a char type, such as:

float i = 2;
switch (i)//will be faulted because I is not one of the int or char

The output range of math.random () is [0, 1]

Algorithm 1:
    a training center to arrange a room for the new students, assume that there are X students, each room can live 6 people, let you use a formula to calculate the number of rooms they want to live.
      Answer: (x+5)/6. This algorithm can also be used to view the paging display of the message board: where x is the total number of messages, 6 is the number of messages per page, the result is the total number of pages.
//If it is x/6+1, then if the problem is 30, there should be 5, but this algorithm is 6.

Algorithm 2:
x=0;
while (true)
{x= (x+1)%10
SYSTEM.OUT.PRINTLN (x);
}
The algorithm realizes 0~9 continuous cyclic output
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instanceof Check if it is an object of the class
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<< left to right 0 (left 1 bit is *2)
>> Right If the left is moved out of place, the original is 0 to make up 0, the original 1 on the 1 (right to move one is/2)
>>> unsigned Right Move no matter what the top number is, always fill 0
operands to int type will be automatically converted to int type and then shifted (Byte,short,char)
The displacement of int cannot exceed 32 digits, a>>33 and a>>1 result is same, a>>32 result is same as original
Long shift cannot exceed 64 digits
y=10
System.out.println (integer.tohexstring (y));
Integer.tohexstring (y) converts an integer y to a hexadecimal number

System.out.println (Float.intbitstofloat (0x50000000)); Prints a floating point number with a 16 in. 50000000.

Integer type, the maximum can move 31 bits, if greater than 31 bits, the shift of the number of modulo, and then move, if the a>>32 bit equivalent to a shift 0 bit, and a>>33 bit, the equivalent of a shift 1 bit, because the plastic has 32
Long plastic shift cannot exceed 64 digits
The shift does not change the value of the variable itself. If a>>1; exist alone in a single line of statements, meaningless

X<<2 equivalent to x* (2 of 2 times)
X>>2 equivalent to x/(2 of 2 times)

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for (i=0;i<10;i++)
{System.out.println (i);}

The For statement can be written as
int i=0;
for (;i<10;)
{System.out.println (i);
i++;
}
can also be written
int i=0;
for (;;)
{if (i>=0)
Break
System.out.println (i);
i++;
}
-------------
St:while (True)
{while (true)
{Break St; Jump out of the while loop
}
}

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After the array is defined, the default initial value is 0
int x[]=new int[5];
int x[]={3,4,5}//To assign an initial value to an array
int X[]=new int[]{3,4,5}

int a[5]; When declaring an array, you cannot specify its length, and an error occurs at compile time

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Int[] x;
X=new int[100];
X=null;
x[0]=2; The run-time error occurs because X is already pointing to null, so X is no longer pointing to heap space and cannot assign a value to X[0]
System.out.println (x.length); To find the length of an X array

Int[][] Xx={{3,2,7},{1,5},{6}}; The initial initialization of two-dimensional arrays

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Int[] X=new int[]{3,1,2,4};
Java.util.Arrays.sort (x); To sort an array of x
Int[] Y=new int[10]; This y must be first made, below to test the beta
System.arraycopy (x,0,y,0,4); Starting with the No. 0 element of X, the No. 0 element of y begins, and the 4 elements in X are examined.