02. java 基本数据类型

Java的基本的数据类型一共有8种

String 不是一个基础数据类型,String是一个char数组 char[]

类型 说明 范围 默认值
byte 8比特类型 (-128 to 127)-2^7 to 2^7-1 0
short 16比特类型 (–32,768 to 32,767)-2^15 to 2^15-1 0
int 32比特类型 (–2,147,483,648 to 2,147,483,647)-2^31 to 2^31-1 0
long 64比特类型 (–9,223,372,036,854,775,808 to 9 ,223,372,036,854,775,807)-2^63 to 2^63-1 0L
float 32比特类型,符合IEEE 754标准的浮点数 (±1.4E-45 to ±3.4028235E38) 0.0f
double 64比特类型,符合IEEE 754标准的浮点数 (±4.9E-324 to ±1.7976931348623157E308) 0.0d
boolean 1 比特 只有两种值true,false false
char 16比特类型 unsigned integer (0 — 65535)
'u0000'

计算机单位换算

1 byte = 8 bits. 
1 kilobyte (K / Kb) = 2^10 bytes = 1,024 bytes.
1 megabyte (M / MB) = 2^20 bytes = 1,048,576 bytes. 
1 gigabyte (G / GB) = 2^30 bytes = 1,073,741,824 bytes.

写个例子来感觉下数据类型
BasicType.java

/**
java-er.com
learn java is so easy
Basic Type
*/
 
public class BasicType {
	public static void main(String[] args){
		byte b = 10; // b < 127 and  b >-128
		System.out.println(b);
 
		short s = 10;
		System.out.println(s);
 
		int i = 3;
		System.out.println(i);
 
		long l = 199999999L;
		System.out.println(l);
 
		float f = 2.34f;
		System.out.println(f);
 
		double d = 3.1415926;
		System.out.println(d);
 
		boolean bx = true;		
		System.out.println(bx);
 
		char c = 97;  //97 equals 'a'
		char c1 = 'a';
		System.out.println(c);
		System.out.println(c1);
	}
}

命令行:

javac BasicType.java
 java BasicType
10
10
3
199999999
2.34
3.1415926
true
a
a

String(字符串) 是一个常用的类型, String 类型用双引号括起来。

String s1 = "My name is ";
String s2 = new String("Jack");
String s3 = s1 + s2;
System.out.println(s3);

输出

My name is Jack


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