2 bytes, range: 0-65535 CHAR Data type can store any character:

Char a = ‘a’; // Add single quotation marks to any single character. Char a = ‘middle’; // Add single quotation marks to any single Chinese character. char a = 111; / / integer. 0 ~ 65535. Decimal, octal, hexadecimal can be. The corresponding character in the output character encoding table.

Note: char can only hold a single character.

char c1 = 'a';
char c2 = 97; Output: A aCopy the code

Int a = 123; long b = 9999999999; // Error, right side is int, but out of range

2. Byte A = 127 can be assigned to integers shorter than the range of int. Byte b = 128; // this is an int

Double a = 3.14; Float b = 3.14; float b = 3.14; // The right literal is of type double, but the left is defined as float

4. Suffix L long long a = 9999999999L; // This is correct

F float float float a = 3.14f;

D double

double a = 3.0;

double a = 3D;

The binary prefix is 0B. The octal prefix is 0. The decimal prefix is 0x

We can print 11 in different bases in our program

tv.setText("Binary:"+0b11+"\n"+
                "Octal:"+011+"\n"+
                "Decimal system:"+11+"\n"+
                "Hex:"+0x11+"\n");
Copy the code

Run the program and the result is as follows:

Binary numbers are represented in binary as follows, advancing 1 for every 2

00000000 — — — — — — — — 0 00000001 — — — — — — — — 1 — — — — — — — 00000010-2, 00000011 — — — — — — — — 3, 00000100 — — — — — — — — 4… 11111111 — — — — — — — — 255

Since the left bit in Java does not participate in counting but is used to represent positive and negative numbers, 0 for positive numbers and 1 for negative numbers, the range of byte is as follows

10000000 — — — — — — — — — 128… 11111101 — — — — — — — — – 3, 11111110 — — — — — — — — — 2, 11111111 — — — — — — — — — 00000000 — — — — — — — — 1 0… 01111111 — — — — — — — — 127

Binary to decimal 01111111 converted to decimal number can be calculated like this, each digit after the number of digits multiplied by 2 power, so the calculation process is as follows:

26 + 1 * 1 * 25 23 + 1 + 1 + 1 * * 24 * 21 + 22 + 1 * 1 * 20 = 127

Common binary and decimal conversion 1 1 10 2 8 32 1000000 64 10000000 128 100000 100 1000

The rule is simple: for every zero added to binary, the decimal result is multiplied by two. The reason is simple: the analogy is decimal, which multiplies by ten for every zero added to it. That makes sense.

Binary to hexadecimal In mathematics, hexadecimal is a system of 1 – digits in 16. It is usually represented by numbers 0 to 9 and letters A to F (or A to F), where A to F indicates 10 to 15. These are called hexadecimal numbers

Every four bits in binary can be represented by one bit in hexadecimal, for example: binary: 0101-> hexadecimal: 5 This is easy to calculate, as we talked about binary 100-> decimal 4. So binary 101-> decimal 5. So 0101 is a decimal 5. Since the hexadecimal 0123456789abcdef represents decimal numbers from 0 to 15, binary: 0101-> hexadecimal: 5

Binary: 1101-> hexadecimal: d Similarly. According to the binary to decimal method, 1101 represents decimal 13, while d represents 13 in hexadecimal

Binary to octal octal is a counting method based on eight digits, 0,1,2,3,4,5,6,7, carried by one

Every three bits in binary can be represented by one bit in octal for 000, 0, 101, 5

‘\u0061’ decimal 97, which stands for a, must be written in two full bytes, so it is summed up as follows: 1. All other decimal digits can be calculated as follows: 1. Hex \u0061 to decimal 1*160+6×161+0x162+0x163=97 1*160+6×161+0x162+0x163=97 2. Divide the number to be converted by the number to be converted to obtain the quotient and remainder 97 ÷ 16 = 6 + 1, so the hexadecimal 61, must write the whole two bytes, plus the prefix that is \u0061 3, other base to other base, can let decimal as the medium

Of course, it doesn’t matter if you can’t remember it, you can convert it directly online

Small data range -> large data range direct conversion can be

byte a = 127;
int b = a;
Copy the code

byte a = -128;
int b = a;
Copy the code

Large data range -> Small data range requires a cast character to implement the cast

int a = 127;
byte b = (byte)a;
Copy the code

In our first Android application yesterday, we put a TextView control inside the layout, the XML file

<TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
Copy the code

Then place the following code in the Activity’s onCreate method

        TextView tv = findViewById(R.id.textView1);
        byte a = -128;
        byte b = 127;

        short c = Short.MIN_VALUE;
        short d = Short.MAX_VALUE;

        int e = Integer.MIN_VALUE;
        int f = Integer.MAX_VALUE;

        long g = Long.MIN_VALUE;
        long h = Long.MAX_VALUE;
        
        float i = Float.MAX_VALUE;
        float j = Float.MIN_VALUE;

        Double k = Double.MAX_VALUE;
        Double l = Double.MIN_VALUE;

        tv.setText(String.valueOf(a));
        tv.append("\n"+b);
        tv.append("\n"+c);
        tv.append("\n"+d);
        tv.append("\n"+e);
        tv.append("\n"+f);
        tv.append("\n"+g);
        tv.append("\n"+h);
        tv.append("\n"+i);
        tv.append("\n"+j);
        tv.append("\n"+k);
        tv.append("\n"+l);
Copy the code

The results of running the program are as follows:



The minimum and maximum values of Float and Double are printed in scientific notation, endingE + digitalIt tells us how many powers of 10 we have to multiply the number before E. Such as3.14 e3So 3.14 x 103 = 3,140, 3.14E-3 = 3.14 x 10-3 =0.00314.

So 1.4E-45 represents 1.4 x 10-45

XML code

    <EditText
        android:id="@+id/et"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Input fall time" />

    <Button
        android:id="@+id/btn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="doClick"
        android:text="Find the landing range." />

    <TextView
        android:id="@+id/tv"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
Copy the code

Java code

 public void doClick(View view) {
        TextView tv = findViewById(R.id.tv);
        EditText et = findViewById(R.id.et);

        Double t = Double.parseDouble(et.getText().toString());
        Double d = 0.5 * 9.8 * t * t;

        tv.setText("Landing distance is + d);
    }
Copy the code

Run the program and the result is as follows: