你真的了解For循环吗？一道For循环Java面试题引发的思考

/**
 * Created by baiguantao on 2017/10/20.
 */
public class T {    
public  static boolean  testA(char a){
        System.out.print(a);        
        return true;

    }    /**
     * for循环的一些疑问
     * @param args
     */
    public static void main(String[] args) {        
        int i=0;        
        for (testA('a');testA('b')&&(i<2);testA('c')) {
            i++;
            testA('d');
        }
    }
}

C:\Users\temp\IdeaProjects\mix_learn\target\classes>
javap -c T.class
Compiled from "T.java"
public class T {  
public T();
    Code:       
       0: aload_0       
       1: invokespecial #1  // Method java/lang/Object."<init>":()V
       4: returnpublic static boolean testA(char);
    Code:       
       0: getstatic     #2  // Field java/lang/System.out:Ljava/io/PrintStream;
       3: iload_0       
       4: invokevirtual #3  // Method java/io/PrintStream.print:(C)V
       7: iconst_1       
       8: ireturn  
public static void main(java.lang.String[]);
    Code:       
       0: iconst_0       
       1: istore_1       
       2: bipush        97
       4: invokestatic  #4  // Method testA:(C)Z
       7: pop
       8: bipush        98
      10: invokestatic  #4  // Method testA:(C)Z
      13: ifeq          39
      16: iload_1      
      17: iconst_2      
      18: if_icmpge     39
      21: iinc          1, 1
      24: bipush        100
      26: invokestatic  #4  // Method testA:(C)Z
      29: pop
      30: bipush        99
      32: invokestatic  #4  // Method testA:(C)Z
      35: pop
      36: goto          8
      39: return
}

C:\Users\temp\IdeaProjects\mix_learn\target\classes>
javap -c T.class
Compiled from "T.java"
public class T {  
public T(); // 这里是默认生成的无参构造函数部分开始
    Code:       
       0: aload_0       //表示对this的操作
       1: invokespecial #1  // Method java/lang/Object."<init>":()V   调用特殊实例方法
       4: return             // 返回结果 
                    // 这里是默认生成的无参构造函数部分结束
  public static boolean testA(char);// 这里是我们写入的静态方法
    Code:       
       0: getstatic     #2 // Field java/lang/System.out:Ljava/io/PrintStream;   System.out调用类方法
       3: iload_0          //从局部变量表中加载int型的数据到操作数栈
       4: invokevirtual #3 // Method java/io/PrintStream.print:(C)V  调用实例方法
       7: iconst_1         //int类型0进栈 
       8: ireturn          // 返回结果

  public static void main(java.lang.String[]);
    Code:       
       0: iconst_0        //int类型0进栈 
       1: istore_1        // int类型1出栈
       2: bipush        97   // byte型常量97（a）进栈
       4: invokestatic  #4   // Method testA:(C)Z  执行静态方法testA
       7: pop                // 栈顶数值出栈(不能是long/double)
       8: bipush        98   // byte型常量98（b）进栈
      10: invokestatic  #4   // Method testA:(C)Z  执行静态方法testA
      13: ifeq          39   //判断语句  是否相等  循环结束 跳转到39
      16: iload_1            //从局部变量表中加载int型的数据到操作数栈
      17: iconst_2           //int类型2进栈 
      18: if_icmpge     39   //比较栈顶两int型数值大小，当结果大于等于0时跳转到39的位置 
      21: iinc          1, 1 //给局部变量表的1号位置的int值增加1
      24: bipush        100  // byte型常量100（d）进栈 
      26: invokestatic  #4   // Method testA:(C)Z  执行静态方法testA
      29: pop                // 栈顶数值出栈(不能是long/double)
      30: bipush        99   // byte型常量99（c）进栈 
      32: invokestatic  #4   // Method testA:(C)Z 执行静态方法testA
      35: pop                // 栈顶数值出栈(不能是long/double)
      36: goto          8    // 重新循环 到8的位置
      39: return             //退出循环
}