[Java] 常用类-02 基础数据类型包装类 / Math 类

public class TestParser {
public static void main(String[] args) {
Integer i = new Integer(100);
Double d = new Double("123.456");
int j = i.intValue() + d.intValue();
float f = i.floatValue() + d.floatValue();
System.out.println(j);
System.out.println(f);
double pi = Double.parseDouble("3.1415926");
double r = Double.valueOf("2.0").doubleValue();
double s = pi * r * r;
System.out.println(s);
try {
int k = Integer.parseInt("1.25");
} catch (NumberFormatException e) {
System.out.println("数据格式不对");
}
System.out.println(Integer.toBinaryString(123) + "B");
System.out.println(Integer.toHexString(123) + "H");
System.out.println(Integer.toOctalString(123) + "O");
}
}

1111011B

7bH

173 O

public class ArrayParser {
public static void main(String[] args) {
double[][] d;
String s = "1,2;3,4,5;6,7,8";
String[] sFirst = s.split(";");
d = new double[sFirst.length][];
for (int i = 0; i < sFirst.length; i++) {
String[] sSecond = sFirst[i].split(",");
d[i] = new double[sSecond.length];
for (int j = 0; j <sSecond.length; j++) {
d[i][j] = Double.parseDouble(sSecond[j]);
}
}

for (int i = 0; i <d.length; i++) {
for (int j = 0; j < d[i].length; j++) {
System.out.print(d[i][j] + " ");
}
System.out.println();
}
}
}

1.0 2.0

3.0 4.0 5.0

6.0 7.0 8.0

public class TestMath {
public static void main(String[] args) {
double a = Math.random();
double b = Math.random();
System.out.println(Math.sqrt(a*a + b*b));
System.out.println(Math.pow(a, 8));
System.out.println(Math.round(b)); // re long
System.out.println(Math.log(Math.pow(Math.E, 15)));
double d = 60.0, r = Math.PI / 4;
System.out.println(Math.toRadians(d));
System.out.println(Math.toDegrees(r));
}
}

1.0152118816776885

0.004305269426978659

1

15.0

1.0471975511965976

45.0