thinking in java——操作符

一.
String类支持+和+=
+号意味着字符串连接，当String+非String元素时，将非String元素转换为String
二.别名现象

class Tank {
  int level;
}   

public class Assignment {
  public static void main(String[] args) {
    Tank t1 = new Tank();
    Tank t2 = new Tank();
    t1.level = 9;
    t2.level = 47;
    print("1: t1.level: " + t1.level +
          ", t2.level: " + t2.level);
    t1 = t2;
    print("2: t1.level: " + t1.level +
          ", t2.level: " + t2.level);
    t1.level = 27;
    print("3: t1.level: " + t1.level +
          ", t2.level: " + t2.level);
  }
} /* Output:
1: t1.level: 9, t2.level: 47
2: t1.level: 47, t2.level: 47
3: t1.level: 27, t2.level: 27
*///:~

三.自动递增和自动递减
前缀递增和前缀递减，先执行运算再生成值，后缀递增和后缀递减，先生成值再运算

public class AutoInc {
  public static void main(String[] args) {
    int i = 1;
    print("i : " + i);
    print("++i : " + ++i); // Pre-increment
    print("i++ : " + i++); // Post-increment
    print("i : " + i);
    print("--i : " + --i); // Pre-decrement
    print("i-- : " + i--); // Post-decrement
    print("i : " + i);
  }
} /* Output:
i : 1
++i : 2
i++ : 2
i : 3
--i : 2
i-- : 2
i : 1
*///:~

四.指数计数法要注意事项
通常将指数作为双精度数来处理（double），如果声明float expDouble3 = 1e-43，会出错提示，不能将double转为float

public class Exponents {
  public static void main(String[] args) {
    // Uppercase and lowercase 'e' are the same:
    float expFloat = 1.39e-43f;
    expFloat = 1.39E-43f;
    System.out.println(expFloat);
    double expDouble = 47e47d; // 'd' is optional
    double expDouble2 = 47e47;
    float expDouble3 = 1e-43;// Automatically double
    System.out.println(expDouble);
  }
}

五.三元操作符

static int ternary(int i) {
    return i < 10 ? i * 100 : i * 10;
  }
  static int standardIfElse(int i) {
    if(i < 10)
      return i * 100;
    else
      return i * 10;
  }

比较简练，高效率编程
六.截尾和舍入
public class CastingNumbers {
public static void main(String[] args) {
double above = 0.7, below = 0.4;
float fabove = 0.7f, fbelow = 0.4f;
print(“(int)above: ” + (int)above);
print(“(int)below: ” + (int)below);
print(“(int)fabove: ” + (int)fabove);
print(“(int)fbelow: ” + (int)fbelow);
}
} /* Output:
(int)above: 0
(int)below: 0
(int)fabove: 0
(int)fbelow: 0
*///:~
Math.round()方法

public class RoundingNumbers {
  public static void main(String[] args) {
    double above = 0.7, below = 0.4;
    float fabove = 0.7f, fbelow = 0.4f;
    print("Math.round(above): " + Math.round(above));
    print("Math.round(below): " + Math.round(below));
    print("Math.round(fabove): " + Math.round(fabove));
    print("Math.round(fbelow): " + Math.round(fbelow));
  }
}