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1. Variables
1. You can modify the data stored in it through the logo;
2. Application format: data type name; as shown in the figure:
Remember that assignment means overwriting, which will overwrite the value inside; for example:
//assignment means overwriting= means overwriting the old value int age=100;
age=90;
age=70;
age=10;
//the final value of age is 10 int age=100;
System.out.println(age);
age=90;
System.out.println(age);
age=70;
System.out.println(age);
age=10;
System.out.println (age);
3. Input name requirements: the preceding letters are lowercase;
4. Apply for a storage space of a data type to the memory, and the contiguous byte memory of the corresponding bytes of the data type will be allocated, as shown in the figure:
two. Constant
1. The identifier can be set to point to a data for the first time, and cannot be modified later;
2. Application format: final data type name;
such as: final int AGE=100; //AGE=10; quadratic value final float FF;
FF=10.5F;
final int AGE=100;
final float FF;
FF=10.5F;
final byte A,B,C,D,E,F;
A=65;
B=10;
C =89;
E=100;
F=-120;
3. The constant does not need to be given a value when applying, but it can be given before use, but remember that it can only be given once;
4. Input name requirements: it must be all uppercase;
5. The constant name usually points to a memory address, as shown in the figure:
three. Matters needing attention: 1. Whether it is a variable or a constant, it is just an identification symbol, and this identification symbol will point to a memory address;
2. No matter what the name is named, it starts with a letter or underscore, and can end with a number;
3. The same name cannot be applied for within the same area (within a curly bracket);
4. Values also have types: after some values are assigned to data types Incompatible, the assignment format is different; ①Integer
int ; ②Decimal
double;
③'' char;
④"" String;
⑤true|false boolean; The
decimal type
⑦ long cannot accept long integers within its own range, because all integers are of type int, and the int type can be up to 2.1 billion;
As shown in the figure:
5. Common data types: byte int double boolean.