010—JAVA包装类型比基本数据类型多的功能

System.out.println(11);
System.out.println(0B11);//0b/B 2进制
System.out.println(011);//0开头 8进制
System.out.println(0x11);//0x/X 16进制

//将10进制转为 2进制
        String toBinaryString = Integer.toBinaryString(5);

        System.out.println("toBinaryString = " + toBinaryString);
        //将10进制转为 8进制
        String toOctalString = Integer.toOctalString(11);

        System.out.println("toOctalString = " + toOctalString);

        //将10进制转为 16 进制
        String toHexString = Integer.toHexString(11);

        System.out.println("toHexString = " + toHexString);

比较两个数大小，求两个数最大值，较小值，各个数据类型的最大值最小值常量

//比较两个整数
        int compare = Integer.compare(100, 30);
        System.out.println("compare = " + compare);

        int max = Integer.max(20, 30);
        System.out.println("max = " + max);
        System.out.println("Integer.min(10, 30) = " + Integer.min(10, 30));


        System.out.println("Integer.MAX_VALUE = " + Integer.MAX_VALUE);

        System.out.println("Integer.MIN_VALUE = " + Integer.MIN_VALUE);

基本数据类型   与 String之间的转换

(转换成什么类型，就用谁.的方式调用方法     如：

基本数据类型---> String       String.valueOf(基本数据类型的值); String----> 基本数据类型

• Byte.parseByte();
• Short.parseShort();
• Integer.parseInt();
• Long.parseLong();
• Float.parseFloat(); 、
• Double.parseDouble();

String --> char     字符串.charAt(下标)

@Test
    public void test04(){

        String s = "中";

        char c = s.charAt(0);
        System.out.println("c = " + c);


    }

 @Test
    public void test03(){

        String s = "3.14";
        double v = Double.parseDouble(s);
        System.out.println("v = " + v);//3.14


        float v1 = Float.parseFloat(s);
        System.out.println("v1 = " + v1);
        String s1 = "true";
        boolean b = Boolean.parseBoolean(s1);

        System.out.println("b = " + b);


    }

注意：         如果是字符串转成基本数据类型  如Integer，必须是纯数字字符串 如果不是 报错 NumberFormatException "10A"; String m = "10A"; int i = Integer.parseInt(m)

public Integer(String s) throws NumberFormatException {
        this.value = parseInt(s, 10);
    }

@Test
    public void test01(){
        int m = 10;
        String s = ""+m;
        System.out.println("s = " + s);


        String s1 = String.valueOf(m);
        System.out.println("s1 = " + s1);

        double d = 3.14;

        String s2 = String.valueOf(d);

        System.out.println("s2 = " + s2);

        byte b = 100;

        String s3 = String.valueOf(b);





    }
}