CS61B Spring 2014 | Lecture Notes | 4. Types/Conditionals
这是我学习CS61B Spring 2014第四课整理的笔记，先记录下来课堂内容以便后期复习，希望大家学习愉快！
课堂内容版权为伯克利CS61B所有
课堂链接：https://www.bilibili.com/video/BV1vt411W7yu?p=3
Primitive Types
-built right into Java
-core to the language
-no need to create an object to store a primitive type
-can be stored in a local variable
byte: 8-bit integer
short: 16-bit
int: 32-bit
long: 64-bit; long x = 43L;
double: a 64-bit floating-point number
float: 32-bit, less accurate
boolean: “true” or “false”
char: a character
double & float values must have a decimal point:
double y = 18.0;
float f = 43.9f;
| Object Types | Primitive Types | |
|---|---|---|
| Contains a | reference | value |
| How defined? | class definition | built into Java |
| How created? | “new” | “6”, “3.4”, “true” |
| How initialized? | constructor | default (usually zero) |
| How used? | method | operators ("+", “*”) |
Create和initialize的区别：
-create: 让这个事物存在
-initialize: 决定这块内存用来储存什么
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java.lang library:
-Math class x = Math.abs(y);
-Integer class int x = Integer.parseInt("1984");
-Double class double d = Double.parseDouble("3.14");
Java library 和 API 区别：
API is a description of all the methods that are in the library that can be called
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Integers can be assigned to variables of longer types
int i = 43;
long l = 43;
i = (int)l; //this is called cast
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Boolean values
boolean x = 3 == 5; // x is false
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”Switch“ statements
switch (month) {
case = 2:
days = 28;
break; //jumps to end of the "switch" statement
case = 4:
case = 6:
case = 9：
case = 11:
days = 30;
break;
default:
days = 31;
break;
}
如果别的条件不符合的话，java会选择default
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The “return” keyword
-causes a method to end immediately
-control returns to the calling method
Prints numbers from 1 to x:
public static void oneToX(int x) {
if (x < 1) {
return;
}
oneToX(x - 1);
System.out.println(x);
-Return也可以用来让一个function返回值
-function: method declared to return a non-void type
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Iteration: a pass through the loop body