Java中按值调用和按引用调用
按值调用意味着调用以参数为值的方法。通过此操作，参数值将传递给参数。
而“按引用调用”是指以参数为参考来调用方法。通过此操作，参数引用将传递给参数。
在按值调用中，对传递的参数所做的修改不会反映在调用者的作用域中，而在按引用进行的调用中，对传递的参数所做的修改是持久性的，而更改则反映在调用者的作用域中。
以下是按值调用的示例-
以下程序显示了通过值传递参数的示例。即使在方法调用之后，参数的值仍保持不变。
示例-按值致电
public class Tester{
public static void main(String[] args){
int a = 30;
int b = 45;
System.out.println("Before swapping, a = " + a + " and b = " + b);
//调用交换方法
swapFunction(a, b);
System.out.println("\n**Now, Before and After swapping values will be same here**:");
System.out.println("After swapping, a = " + a + " and b is " + b);
}
public static void swapFunction(int a, int b) {
System.out.println("Before swapping(Inside), a = " + a + " b = " + b);
//用n2交换n1-
int c = a;
a = b;
b = c;
System.out.println("After swapping(Inside), a = " + a + " b = " + b);
}
}输出结果
这将产生以下结果-
Before swapping, a = 30 and b = 45 Before swapping(Inside), a = 30 b = 45 After swapping(Inside), a = 45 b = 30 **Now, Before and After swapping values will be same here**: After swapping, a = 30 and b is 45
示例-通过引用致电
Java在传递引用变量的同时也仅使用按值调用。它创建引用的副本，并将它们作为有值的方法传递给方法。由于引用指向对象的相同地址，因此创建引用副本是没有害处的。但是，如果将新对象分配给引用，则不会反映出来。
public class JavaTester {
public static void main(String[] args) {
IntWrapper a = new IntWrapper(30);
IntWrapper b = new IntWrapper(45);
System.out.println("Before swapping, a = " + a.a + " and b = " + b.a);
//调用交换方法
swapFunction(a, b);
System.out.println("\n**Now, Before and After swapping values will be different here**:");
System.out.println("After swapping, a = " + a.a + " and b is " + b.a);
}
public static void swapFunction(IntWrapper a, IntWrapper b) {
System.out.println("Before swapping(Inside), a = " + a.a + " b = " + b.a);
//用n2交换n1-
IntWrapper c = new IntWrapper(a.a);
a.a = b.a;
b.a = c.a;
System.out.println("After swapping(Inside), a = " + a.a + " b = " + b.a);
}
}
class IntWrapper {
public int a;
public IntWrapper(int a){ this.a = a;}
}这将产生以下结果-
输出结果
Before swapping, a = 30 and b = 45 Before swapping(Inside), a = 30 b = 45 After swapping(Inside), a = 45 b = 30 **Now, Before and After swapping values will be different here**: After swapping, a = 45 and b is 30