学习笔记之基本数据类型-包装类-String之间的转换

基本类型              包装类                String类

int->Integer   :             Integer构造器

Integer-> int  :   Integer.intValue()方法

int -> String  :  Integer.toString方法，String.valueof()方法

String -> int  :  Integer.parseInt()方法

Integer -> String : Integer.toString()方法，String.valueof()方法

String -> Integer : Integer的构造器,Integer.valueof()方法

5.0以后  自动拆装箱

例如：

Integer iobj1 = 10; // 装

int j = iobj1;  //拆

public class TestDemo {
    public static void intDemo() {
        // int->String
        // String -> int
        int a = 3;
        System.out.println(a);
        String a1 = Integer.toString(a);
        System.out.println(a1);
        int a2 = Integer.parseInt(a1);
        System.out.println(a2 - 4);

        // int -> Integer
        // Integer -> int
        Integer a3 = a;
        int a4 = a3.intValue();
        System.out.println(a3);
        System.out.println(a4);

        // Integer -> String
        // String -> Integer
        Integer i = new Integer(10);
        String a5 = i.toString();
        System.out.println(a5);
        Integer i2 = Integer.valueOf(a5);
        Integer i3 = Integer.parseInt(a5);
        System.out.println(i2 + 5);
        System.out.println(i3 + 7);

    }
    

    public static void floatDemo(){
        //float->Float
        //Float->float
        float f1 = 1.20f;
        Float f2 = f1;
        float f3 = f2;
        System.out.println(f2 +"	" + f3);
        
        //float -> String
        //String -> float
        float f4 = 2.234f;
        String f5 = Float.toString(f4);
        System.out.println(f5 + 7);
        f4 = Float.parseFloat(f5);
        System.out.println(f4);
        
        //Float -> String
        //String -> Float
        Float f6 = new Float(12.4);
        String f7 = Float.toString(f6);
        System.out.println(f7 + 9);
        f6 = Float.parseFloat(f7);
        System.out.println(f6 + 1.1f);
    }
    
    public static void charDemo(){
        //char -> Character
        //Character -> char
        char ch = 'p';
        Character ch2 = new Character('q');
        ch2 = ch;
        System.out.println(ch2);
        ch = new Character('u');
        System.out.println(ch);
        
        //char -> String
        //String -> char
        char ch3 = 'q';
        String ch4 = Character.toString(ch3);
        System.out.println(ch4);
        char ch5 = ch4.charAt(0);
        System.out.println(ch5);
        
        //Character -> String
        //String -> Character
        Character ch6 = new Character('a');
        String ch7 = ch6 + "";
        System.out.println(ch7);
        Character ch8 = Character.valueOf(ch6);
        System.out.println(ch8);
    }
    
    public static void main(String[] args) {
        TestDemo.intDemo();
    }

}