java - 不明白简单java程序的输出

Question

public class Test10 
{ 
  public static void main( String[] args ) 
  { 
    Thing2 first = new Thing2( 1 ); 
    Thing2 second = new Thing2( 2 ); 
    Thing2 temp = second; 
    second = first; 
    first = temp; 
    System.out.println( first.toString() ); 
    System.out.println( second.toString() ); 
    Thing2 third = new Thing2( 3 ); 
    Thing2 fourth = new Thing2( 4 ); 
    third.swap1( fourth ); 
    System.out.println( third.toString() ); 
    System.out.println( fourth.toString() ); 
    second.setCount( fourth.getCount() ); 
    third = first; 
    System.out.println( third == first ); 
    System.out.println( fourth == second ); 
    System.out.println( first.toString().equals( third.toString() ) ); 
    System.out.println( second.toString().equals( fourth.toString() ) ); 
    System.out.println( first.toString() ); 
    System.out.println( second.toString() ); 
    System.out.println( third.toString() ); 
    System.out.println( fourth.toString() ); 
    first = new Thing2( 1 ); 
    second = new Thing2( 2 ); 
    first.swap2( second ); 
    System.out.println( first.toString() ); 
    System.out.println( second.toString() ); 
  } 
} 



class Thing2 
{ 
  private int count; 

  public Thing2( int count ) 
  { 
    this.count = count; 
  } 
  public int getCount() 
  { 
    return this.count; 
  } 
  public void setCount( int count ) 
  { 
    this.count = count; 
  } 
  public String toString() 
  { 
    String s = " "; 
    switch( this.count ) 
    { 
      case 1: 
        s = s + "first ";  
      case 2: 
        s = s + "mid "; 
        break; 
      case 3: 
        s = s + "last "; 
        break; 
      default: 
        s = s + "rest "; 
        break; 
    } 
    return s; 
  } 
  public void swap1( Thing2 t2 ) 
  { 
    int temp; 
    temp = this.getCount(); 
    this.setCount( t2.getCount() ); 
    t2.setCount( temp ); 
  } 
  public void swap2( Thing2 t2 ) 
  { 
    Thing2 temp; 
    Thing2 t1 = this; 
    temp = t1; 
    t1 = t2; 
    t2 = temp; 
  } 
} 

Given the following definition of class Thing2, what is the output of the Java application Test10?

嘿伙计们，这是我的一门课。有两个类(上面列出):Thing2 和 Test10。这是输出，但我不明白如何获得输出(即什么指向什么以及所有内容得到解决的顺序是什么？)。谢谢!

mid
first mid
rest  
last
true
false
true
true 
mid  
last 
mid 
last
first mid
mid

Answer 1

一个技巧是 switch 语句中的 case 1 没有 break 语句，因此代码继续执行 case 2 指令并创建字符串“first mid “而不是 Thing(1) 的“第一个”

像这样向打印语句添加注释可能会有所帮助

System.out.println("First is " + first.toString());
System.out.println("third == first?" + (first == third));

如果您这样做，请添加更多打印语句。

将每个变量视为一个大箭头。

语句a = new Thing(2)创建一个带有单词“mid”的Thing，并将a箭头指向它。

语句a = b采用b箭头所看到的任何内容，并将a箭头指向同一事物。