Javaプログラミングにおけるメソッドパラメータの受け渡しの詳細な分析

public static class Value {
  private String value = "value";
  public String getValue() { return value; }
  public void setValue(String value) { this.value = value; }
}

public static void newValue(Value value) {
  value = new Value();
  value.setValue("new value");
  System.out.println("In newValue, HashCode = " + value.hashCode() + ", value = " + value.getValue());
}
    
public static void modifyValue(Value value) {
  value.setValue("new value");
  System.out.println("In modifyValue, HashCode = " + value.hashCode() + ", value = " + value.getValue());
}

public static void main(String[] args) {
  Value value1 = new Value();
  System.out.println("Before modify, HashCode = " + value1.hashCode() + ", value = " + value1.getValue());
  // 将value1指向新的Value对象
  newValue(value1);
  System.out.println("After modify, HashCode = " + value1.hashCode() + ", value = " + value1.getValue() + "\n");
  Value value2 = new Value();
  System.out.println("Before modify, HashCode = " + value2.hashCode() + ", value = " + value2.getValue());
  // 使用object的set方法，修改对象的内部值
  modifyValue(value2);
  System.out.println("After modify, HashCode = " + value2.hashCode() + ", value = " + value2.getValue());
}

Before modify, HashCode = 12677476, value = value
In newValue, HashCode = 33263331, value = new value
After modify, HashCode = 12677476, value = value
  
Before modify, HashCode = 6413875, value = value
In modifyValue, HashCode = 6413875, value = new value
After modify, HashCode = 6413875, value = new value

newValue{
  Value_ref2 = value_ref1;  // 按值传入引用value_ref1，得到value_ref1的副本
  value_obj2 = new Value();  // value_obj2被创建、初始化在“堆“中
  value_ref2 -> value_obj2;  // value_ref2 指向value_obj2
value_ref2 ->value_obj2.setValue(“xxx”); // value_obj2 的value被修改
printValueObj2();      // 此处打印的是obj2的值
}
modifyValue{
  Value_ref2 = value_ref1;  // 按值传入引用value_ref1，得到value_ref1的副本
value_ref2 ->value_obj1.setValue(“xxx”); // value_obj1 的value被修改
printValueObj1();      // 此处打印的是obj1的值
}

public static void nPrintln(String message, int n) {
 for (int i = 0; i < n; i++)
  System.out.println(message);
}

public class TestPassByValue {
 
  public static void main(String[] args) {
   int num1 = 1;
   int num2 = 2;
 
   System.out.println("Before swap method, num1 is " +
             num1 + " and num2 is " + num2);
 
   // 调用swap方法
   swap(num1, num2);
   System.out.println("After swap method, num1 is " +
             num1 + " and num2 is " + num2);
  }
  /** 交换两个变量的方法 */
  public static void swap(int n1, int n2) {
   System.out.println("\tInside the swap method");
   System.out.println("\t\tBefore swapping n1 is " + n1
              + " n2 is " + n2);
   // 交换 n1 与 n2的值
   int temp = n1;
   n1 = n2;
   n2 = temp;
 
   System.out.println("\t\tAfter swapping n1 is " + n1
              + " n2 is " + n2);
  }
}

Before swap method, num1 is 1 and num2 is 2
    Inside the swap method
        Before swapping n1 is 1 n2 is 2
        After swapping n1 is 2 n2 is 1
After swap method, num1 is 1 and num2 is 2