第4章 控制执行流程(java编程思想)

4,4 Foreach语句

用于迭代数组或字符串中的所有元素

//: control/ForEachString.java

public class ForEachString {
  public static void main(String[] args) {
    for(char c : "An African Swallow".toCharArray() )
      System.out.print(c + " ");
  }
} /* Output:
A n   A f r i c a n   S w a l l o w
*///:~

foreach还可以用与任何Iterable对象 , 例

import static net.mindview.util.Range.*;
import static net.mindview.util.Print.*;

public class ForEachInt {
  public static void main(String[] args) {
    for(int i : range(10)) // 0..9
      printnb(i + " ");
    print();
    for(int i : range(5, 10)) // 5..9
      printnb(i + " ");
    print();
    for(int i : range(5, 20, 3)) // 5..20 step 3
      printnb(i + " ");
    print();
  }
} /* Output:
0 1 2 3 4 5 6 7 8 9
5 6 7 8 9
5 8 11 14 17
*///:~

4.7 臭名昭著的goto

java中没有goto, 只有与goto类似的标签, 标签后面是跟有冒号的标识符, 类似这样.

lebel1;

continue会直接中断内部迭代以及外部迭代, 直接跳转到label处,随后,实际上是继续迭代过程

//: control/LabeledWhile.java
// While loops with "labeled break" and "labeled continue."
import static net.mindview.util.Print.*;

public class LabeledWhile {
  public static void main(String[] args) {
    int i = 0;
    outer:
    while(true) {
      print("Outer while loop");
      while(true) {
        i++;
        print("i = " + i);
        if(i == 1) {
          print("continue");
          continue;
        }
        if(i == 3) {
          print("continue outer");
          continue outer;
        }
        if(i == 5) {
          print("break");
          break;
        }
        if(i == 7) {
          print("break outer");
          break outer;
        }
      }
    }
  }
} /* Output:
Outer while loop
i = 1
continue
i = 2
i = 3
continue outer
Outer while loop
i = 4
i = 5
break
Outer while loop
i = 6
i = 7
break outer
*///:~