J2SE synthesis: A little understanding of final

In the process of programming, we always encounter the final keyword, then we have to final how to understand, the following is a little superficial understanding of me, and you share.

package zy.pro.jbd.demo;
public class FinalDemo {
final　 int　 numInt1=16;
final String　str="zy";
final　String str1;

Note: STR1 is not initialized here, you must initialize it in the constructor, or you will have to make an error. In other words, the final variable must be initialized.

public FinalDemo() {
str1="zy";
}
public static void main(String[] args){
System.out.println("-------------------------------------------------");
}
public void　executeFinalTest(){
}
private　void　testFinalInt(){
numInt1+=1;

Above, we define NUMINT1 as final variable, and an error will occur at the time: cannot assign a final value to final variable numInt1 in line 24

Thus, if a variable of a basic type is defined as final, then this variable will no longer be changed.

System.out.println(numInt1);
}
private void　testFinalString(){
str=str+"aaaaa";

The same error is also shown here.

System.out.println(str);
}
}

Let's make one more test:

(1) First create a class: A.java

package zy.pro.jbd.testbase;
public class A {
int　t=10;
public A() {
}
public void setT(int　t){
this.t=t;
}
public int　getT(){
return this.t;
}
}(2) write the following test code

final A a = new A();
public void testFinalObject() {
a.setT(29);
System.out.println("t:　　 " + a.getT());
}

The results of the test output are:

T:29