java代码练习第3课

三叶草

test018.java

public class test018
{

  public static void main(String[] args)
  {
  int x = 50;
  float y = x;  //隐式转换，int 精度小于 float ，由系统自动完成
  // 顺序参照 byte < short < int < long < float < double
  System.out.println(y);
  byte myByte = 127;
  int myInt = 150;
  float myFloat = 452.12f;
  char myChar = 10;
  double myDouble = 45.46546;
  System.out.println("byte + float = " + (myByte + myFloat));  //float
  System.out.println("byte + int = " + (myByte + myInt)); // int
  System.out.println("byte + char = " + (myByte + myChar)); //int
  System.out.println("char + double=" + (myChar + myDouble));  //double
  //下面是强制转换
  double a = 45.23;
  int b = (int)a; //丢失精度
  double c = 456.6;
  long d = (long)c; //丢失精度
  char e = 'a';
  int f = (int)e; // 
  System.out.println(b);
  System.out.println(d);
  System.out.println(f);
  }

}

test019.java

public class test019
{

  public static void main(String[] args)
  {
  int x = 20;
  {
    int y = 40;  // 花括号表示符合语句，在花括号内部声明的变量，仅在其内部有用，即限定了作用域
    System.out.println("y=" + y);
    int z = 245;
    boolean b;
    {
    b = y > z;
    System.out.println("b = " + b);
    System.out.println("x= " + x);
    }
  }

  String word = "hello world";
  System.out.println(word);
  }

}

test020.java

public class test020
{

  public static void main(String[] args)
  {
  //if else 条件语句
  //语句序列中只有一条语句时,写法如下,但是不建议这样写,没有可读性
  int a = 100;
  if(a== 100)
    System.out.println("a = "  + a);
  //语句序列省略时，可以末尾加分号，代替花括号，依然不建议这样写，可读性差
  boolean b = false;
  if(b);
  boolean c = false;
  if(c) {}

  //
  int x = 45;
  int y = 12;
  if(x > y)
  {
    System.out.println("变量x大于变量y");
  }
  else
  {
    System.out.println("变量x小于变量y");
  }
  //
  int math = 95;
  int english = 56;
  if(math >= 60)
  {
    System.out.println("数学及格了");
  }
  else
  {
    System.out.println("数学不及格");    
  }
  if(english > 59)
  {
    System.out.println("英语及格了");
  }
  else
  {
    System.out.println("英语不及格");    
  }
  //三元运算符替代法
  int a1 = 5;
  int b1 = 0;
  if(a1 > 0)
  {
    b1 = a1;
  }
  else
  {
    b1 = -a1;
  }
  int a2 = 5;
  int b2 = 0;
  b2 = a2 > 0 ? a2:-a2;
  System.out.println("b1 = " + b1);
  System.out.println("b2 = " + b2);

  }

}