Java constants have two meanings, which I will explain separately:

The 1 th meaning is a value, and the value itself, we can call it a constant, and give several examples:

Integer constant: 123

Real constant: 3. 14

Character constant: "a"

Logical constants: true, false

String constant: "helloworld"

This is just talk, for example, the number 7, we can say "an int constant 7"

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There is another one, which was asked by the landlord:

The second layer means immutable variables, also called constants. Grammatically speaking, it is final. You modify a variable with the final keyword, and then as long as it is assigned, it can't be changed, and it can't be assigned again. According to one example:

final int I = 0；

Then the value of this I can never be changed, it can only be 0, so it is an immutable variable. This sentence seems contradictory, but it is not contradictory. This sentence is understood as follows:

I is a variable of type int, and the variable itself is changeable (the value can be changed), but now it is immutable because of the addition of final, so it is immutable.