原 荐 你真的了解For循环吗？一道For循

/**
 * 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: return

  public 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
}