java代码练习第3课

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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);


  }


}

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