Common Java classes - Integer class basic types of packaging

1 Overview

The Integer class wraps a base object type in an int
Integer class provides a number of methods that can convert between types of type int and String

package zhengshu;

public class IntegerDm {
    public static void main(String[] args){
        System.out.println(Integer.toBinaryString(100));//转换成二进制数：1100100
        System.out.println(Integer.toOctalString(100));//转换成八进制数：144
        System.out.println(Integer.toHexString(100));//转换成十六进制数：64
        System.out.println("---------------------------");
        System.out.println(Integer.MAX_VALUE);//代表int所能表示的最大值
        System.out.println(Integer.MIN_VALUE);//代表int所能表示的最小值
    }
}

String type is converted to int type:

package zhengshu;

public class IntegerDm {
    public static void main(String[] args){
        int i1 = 100;
        System.out.println("i1的值为："+i1);
        Integer i2 = new Integer(i1);
        System.out.println("i2的值为："+i2);

        String s1 = "100";
        Integer i3 = new Integer(s1);//字符串转换成数字，前提是这个字符串是由数组字符组成
        System.out.println("i3的值为："+i3);
    }
}

2, the configuration method

public Integer(int value)
public Integer(String s)

3, member methods

public int intValue()
public static int parseInt(String s)
public static String toString(int i)
public static Integer valueOf(int i)
public static Integer valueOf(String s)

package zhengshu;

public class IntegerDm {
    public static void main(String[] args){
        //int -> Stirng
        int i1 = 100;
        String s1 = ""+ i1;//int -> Stirng
        System.out.println(s1);//输出字符串

        String s2 = String.valueOf(i1);//int -> Stirng,返回给定参数的原生 Number 对象值
        System.out.println(s2);

        Integer i2 = new Integer(i1);
        System.out.println(i2);

        String s3 = Integer.toString(i1);
        System.out.println(s3);
        System.out.println("------------------------");

        //String -> int
        String st1 = "200";
        Integer in1 = new Integer(st1);
        System.out.println(in1);

        int in2 = in1.intValue();
        System.out.println(in2);

        System.out.println(Integer.parseInt(st1));//parseInt() 方法用于将字符串参数作为有符号的十进制整数进行解析
    }
}

4, common basic hex conversion

public static String toBinaryString(int i)
public static String toOctalString(int i)
public static String toHexString(int i)

5, decimal to hexadecimal other

public static String toString(int i,int radix)

6, other binary to decimal

public static int parseInt(String s,int radix)

package zhengshu;

public class IntegerDm {
    public static void main(String[] args){
        System.out.println(Integer.toBinaryString(100));//十进制转二进制
        System.out.println(Integer.toOctalString(100));//十进制转八进制
        System.out.println(Integer.toHexString(100));//十进制转十六进制
        System.out.println("---------------------------");

        //十进制转到其他进制
        System.out.println(Integer.toString(100,2));//十进制转二进制
        System.out.println(Integer.toString(100,8));//十进制转八进制
        System.out.println(Integer.toString(100,16));//十进制转十六进制
        System.out.println(Integer.toString(100,7));//十进制转七进制
        System.out.println(Integer.toString(100,30));//十进制转三十进制
        System.out.println("============================");

        //其他进制转到十进制
        System.out.println(Integer.parseInt("100",10));//那个数字的10进制是100，100
        System.out.println(Integer.parseInt("100",2));//那个数字的2进制是100，4
        System.out.println(Integer.parseInt("100",8));//那个数字的8进制是100，64
        System.out.println(Integer.parseInt("100",16));//那个数字的16进制是100，256
    }
}

7, the automatic boxing and unboxing

Integer x = new Integer(4);Can be written Integer x = 4;(autoboxing)
x = x + 5;(Automatic unpacking), by the method intValue
New features JDK 1.5 ( autoboxing ): The basic types to wrapper class type
JDK 1.5 new features ( automatic unpacking ): to convert the base type packaging type

package zhengshu;

public class IntegerDm {
    public static void main(String[] args){
        byte b1 = 100;
        byte b2 = b1;

        Integer i1 = new Integer(200);//定义一个 int 类型的包装类型变量i1
        Integer i2 = 300;
        i2 = i2 + 400;
        System.out.println("i2的值为："+i2);//输出：700

        Integer i3 = Integer.valueOf(500);//自动装箱
        i3 = Integer.valueOf(i3.intValue() + 60);//自动拆箱，再自动装箱
        System.out.println((new StringBuilder("i3的值为：")).append(i3).toString());//输出：560
    }
}

package zhengshu;

public class IntegerDm {
    public static void main(String[] args){
        Integer i1 = new Integer(128);
        Integer i2 = new Integer(128);
        System.out.println(i1 == i2);
        System.out.println(i1.equals(i2));
        System.out.println("-----------------------");

        Integer i3 = 128;
        Integer i4 = 128;
        System.out.println(i3 == i4);
        System.out.println(i3.equals(i4));
        System.out.println("=========================");

        Integer i5 = 127;
        Integer i6 = 127;
        System.out.println(i5 == i6);
        System.out.println(i5.equals(i6));
        System.out.println("+++++++++++++++++++++++++");

        int i7 = 1280;
        Integer i8 = 1280;
        System.out.println(i7 == i8);
        // 针对-128到127之间的数据，做了一个数据缓冲池，如果数据是该范围内的，每次并不创建新的空间
    }
}

note:

Integer data direct assignment, if between -128 to 127, retrieves data directly from the buffer pool
In use, Integer x = null;the above code will be a NullPointerException (null pointer exception)

Common Java classes - Integer class basic types of packaging

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