Java Number class

In general, we use the basic data types of the data: byte, int, short, long, double, float, boolean, char;

There are also eight types of packaging: Byte, Integer, Short, Long, Double, Float, Character, Boolean;

The wrapper types are declared in final and can not be inherited and override; in practice, the compiler automatically boxes the base data type into an object type, or unboxs the object type into a base data type;

public static void main(String[] args) {
	int num1 = 1;
	//将基本数据类型装箱成对象包装类型
	Integer num2 = num1;
	Integer num3 = 3;
	//将对象数据类拆箱
	int num4 = num3;
}

The Number class is an abstract class under the java.lang package that provides a way to unbox the wrapper type into a basic type, and all the wrapper types of the base type (data type) inherit the abstract class, and the final declaration is not inheritable;

package java.lang;

public abstract class Number implements java.io.Serializable {

    public abstract int intValue();

    public abstract long longValue();

    public abstract float floatValue();

    public abstract double doubleValue();

    public byte byteValue() {
        return (byte)intValue();
    }

    public short shortValue() {
        return (short)intValue();
    }

    private static final long serialVersionUID = -8742448824652078965L;
}

This wrapper, which is especially supported by the compiler, is called boxing, so when the built-in data type is used as an object, the compiler boxes the built-in type as a wrapper class. S imilarly, the compiler can unbox an object as a built-in type. The Number class belongs to the java.lang package.

Here is an example of boxing and unboxing:

public class Test{

   public static void main(String args[]){
      Integer x = 5; // boxes int to an Integer object
      x =  x + 10;   // unboxes the Integer to a int
      System.out.println(x); 
   }
}

The above examples compile and run as follows:

15

When x is assigned an integer value, the compiler boxes x because x is an object. Then, in order for x to add, unbox x.

Java Math class

The Math of Java contains properties and methods for performing basic mathematical operations, such as primary exponents, logs, square roots, and triangular functions.

Math's methods are defined as static, and the Math class can be called directly in the main function.

Instance

public class Test {  
    public static void main (String []args)  
    {  
        System.out.println("90 度的正弦值：" + Math.sin(Math.PI/2));  
        System.out.println("0度的余弦值：" + Math.cos(0));  
        System.out.println("60度的正切值：" + Math.tan(Math.PI/3));  
        System.out.println("1的反正切值： " + Math.atan(1));  
        System.out.println("π/2的角度值：" + Math.toDegrees(Math.PI/2));  
        System.out.println(Math.PI);  
    }  
}

The above examples compile and run as follows:

90 度的正弦值：1.0
0度的余弦值：1.0
60度的正切值：1.7320508075688767
1的反正切值： 0.7853981633974483
π/2的角度值：90.0
3.141592653589793

The Number and Math class method

The following table lists common methods for Number and Math classes: