09-2java语言基础

4 5
常量
final int MIN_HEIGHT = 69;
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String 类----1
int length()
import ng.*;
String s = "hello world"; System.out.println ( s.length() ); 输出 11
String fruit = "banana"; String searchString = "an"; int n1 = fruit.indexOf(searchString, 0); int n2 = fruit.indexOf(searchString, n1 + 1); int n3 = fruit.indexOf(searchString, n2 + 1);
num2 = num1;
int
total;
String s 0x0d4fe1a8
name2 = name1; 38 38 name1 name2 "wang"
boolean done = false;
num1 num2
At memory location 0x0d4fe1a8 Hello world
2,输入
需 import java.util. Scanner;
import java.util.*; public class ScannerUsage { public static void main (String args[ ]) { Scanner scan = new Scanner (System.in); System.out.println ("Enter first value "); int x = scan.nextInt(); System.out.println ("Enter second value "); int y = scan.nextInt(); int z = x + y;
alphabet
"abcdefghijklmnopqrstuvwxyz"
s
"sun" "Sun"
c1 c2 c3
'j' 'p' 'c'
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11
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String 类----2
static String valueOf(int i) static String valueOf(double d)
2.4 运算符
Scanner scan = new Scanner (System.in); int x = scan.nextInt(); double d = scan.nextDouble(); String s = scan.next();
scan Scanner:
结果 Person Height Shoe size ========================= Hannah 5'1" 7 Jenna 5'10" 9 JJ 6'1" 14
x
5
d
3.5
s
"hello world"
System.out.println ("The sum of " + x + " and " + y + " is " + z);
}
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char op = scan.next().charAt(0);
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}
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Scanner API
public int nextInt() public short nextShort() public long nextLong() public double nextDouble() public float nextFloat() public String next() public String nextLine() 不读空格 读一行
int v1 = 12; 重载 double v2 = 3.14; String s1 = String.valueOf ( v1 ); String s2 = String.valueOf ( v2 );
System.out.print System.out.println System.out.println System.out.println System.out.println
2.1 基本符号
2.2 基本数据类型
float double boolean char
多行注释 单行注释 文档注释
2
第2章 Java 语言基础
标识符
由字母,数字,_和$组成,且第一个字符必须为 字母,_ 或 $ . 大小写敏感.
实数 true 或 false
值为
注释
/* // 注释部分 */ 注释部分
2.6 控制语句
选择语句:if...else,switch 循环语句:while,for, do...while 转移语句:break,continue
if ( a == '0' ) System.out.println ("zero"); else if (a == '1') System.out.println ("one"); else if (a == '2') System.out.println ("two"); else if (a == '3') System.out.println ("three"); else if (a == '4') System.out.println ("four"); else System.out.println ("five+");
输出
true
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System.out.println("Person\tHeight\tShoe size"); System.out.println("========================="); System.out.println("Hannah\t5'1\"\t7"); System.out.println("Jenna\t5'10\"\t9"); System.out.println("JJ\t6'1\"\t14");
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System.out.println("Enter a number: "); int n1 = scan.nextInt(); System.out.println("Enter another number: "); int n2 = scan.nextInt(); System.out.println("Enter desired operator: "); char operator = scan.next().charAt(0); switch (operator) { case '+' : System.out.println(n1 + n2); break; case '-' : System.out.println(n1 - n2); break; case '*' : System.out.println(n1 * n2); break; case '/' : System.out.println(n1 / n2); break; default: System.out.println("Illegal request"); }
String substring (int beginx, int endx)
String toLowerCase() String toUpperCase() char charAt(int index)
int indexOf(String s,int fromIndex)
String date = "August 21, 1976"; String month = date.substring(0, 6); System.out.println("Month is " + month + ".");
("foo"); ("bar"); (); ("foo"); ("bar");
输出: foobar foo bar
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例
int i = 7;
System.out.println ("result: " + 3/5); – 输出 result: 0 System.out.println ("result: " + 5 % 3);
转义序列
\n \t \\ \" \' 换行 tab 反斜杠 双引号 单引号
System.out.println ("i = " + it: 2
int x = 5; System.out.println (x == 5);
System.out.println ("result: " + 3/5.0); – 输出 result: 0.6
System.out.println("First search: " + n1); System.out.println("Second search: " + n2); System.out.println("Third search: " + n3);