Sharing code examples illustrating Java's delivery and callback mechanism

Java pass by value or by reference
1. Original type parameter passing

public void badSwap(int var1, int var2) 
{
int temp = var1; 
var1 = var2; 
var2 = temp;
}

2. Reference type parameter passing

public void tricky(Point arg1, Point arg2)
{
 arg1.x = 100;
 arg1.y = 100;
 Point temp = arg1;
 arg1 = arg2;
 arg2 = temp;
}
public static void main(String [] args)
{
 Point pnt1 = new Point(0,0);
 Point pnt2 = new Point(0,0);
 System.out.println("X: " + pnt1.x + " Y: " +pnt1.y);
 System.out.println("X: " + pnt2.x + " Y: " +pnt2.y);
 System.out.println(" ");
 tricky(pnt1,pnt2);
 System.out.println("X: " + pnt1.x + " Y:" + pnt1.y);
 System.out.println("X: " + pnt2.x + " Y: " +pnt2.y);
}

Run these two programs, I believe you will understand: Java manipulates objects 'by reference,' but it passes object references to methods 'by value.

java callback mechanism
spring uses the java callback mechanism extensively , the following is a brief introduction to the Java callback mechanism:

In a word, callback is a two-way calling mode. What does it mean? That is, the callee will also call the other party when it is called. This It's called a callback. "If you call me, I will call back."

Look at the following example about the callback mechanism:

Interface CallBackInterface:

public interface CallBackInterface {
 void save();
}

Class ClassB:

public class ClassB implements CallBackInterface {
 
public void save() {
System.out.println("执行保存操作!");
}
//
public void add()
{
 
    //这里调用ClassA的方法 同时ClasssB又会回调ClassB的save方法
    new ClassA().executeSave(new ClassB());
 }
 
}

ClassClassA:

public class ClassA {
 
 public void executeSave(CallBackInterface callBackInterface)
 {
 getConn();
 callBackInterface.save();  //you call me
 realse();
 }
 public void getConn()
 {
 System.out.println("获取数据库连接!");
 }
 public void realse()
 {
 System.out.println("释放数据库连接!");
 }
}

A more classic example of the use of callback functions (using java anonymous classes) omits the source code here

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