全新java初学者实践教程6(Java SE5.0版)
?^7t'`zk 基本语法3
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d 3k\#CiB{ g2BHHL;` 我们这个教程侧重的是实践的内容和语言的重点。在[font="Times]java语言中还有很多细节的东西,请参考[font="Times]sun公司的官方培训教程。我们这里不能一一讲述。这节课我们来给大家提供一些程序流程控制的一些例子供大家学习。计算机怎么做事情,是我们教给他的。我们用它解决实际生活中的问题,所以计算机要描述现实生活中的流程。[font="Times]Java语言中提供了[font="Times]4类程序控制语句,来描述流程:
F}F&T /NLui@|R [font="Times] 1.循环语句[font="Times]:while,do-while,for
h{CL{>d =#;3Q~:Jl^ [font="Times]2.分支语句[font="Times]:if-else,switch,
\K5DOM "# [font="Times]
nL5cK: 3.跳转语句[font="Times] break,continue,label: 和[font="Times]return
J=\HO8E6> [font="Times]
5&QJ7B,! 4.异常处理语句[font="Times]:try-catch-finally,throw
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*>!Z% 实践:
caU0\VS [font="Times] 1.循环语句
'9laa=H%8 [font="Times] while 语句
fa-IhB1!K [font="Times]class While {
N@2dA*T, [font="Times]public static void main(String args[]) {
\z>fb%YW [font="Times]int n = 10;
`nUXDmdwzO [font="Times]while(n > 0) {
),0g~'I~D
[font="Times]System.out.println("tick " + n);
d?ex,f. [font="Times]n--;
gR&Q3jlIV [font="Times]}
R_ B7EP [font="Times]}
B~6&{7xc% [font="Times]}
PY_u/<u [font="Times] do…while 语句
34`'M+3 [font="Times] class DoWhile {
N nRD|A [font="Times]public static void main(String args[]) {
Nkjza:f{ [font="Times]int n = 10;
6g2a[6G5 [font="Times]do {
{o)L c6T8s [font="Times]System.out.println("tick " + n);
qz+dmef [font="Times]n--;
H['N [font="Times]} while(n > 0);
QqDC4+p" [font="Times]}
VyXKZ%\dQ/ [font="Times]}
_G[g;$< 二者区别,[font="Times]do…while至少循环一次,而[font="Times]while的表达式要是为[font="Times]flase的话可以一次也不循环。再通俗一点,[font="Times]do…while就算是括号里的是[font="Times]flase,人家最少也能[font="Times]do一次。
i5en*)O8 [font="Times] for语句
oQLq&zRH`f [font="Times] class ForTick {
h:W;^\J:- [font="Times]public static void main(String args[]) {
V_R@o3kv; [font="Times]int n;
xR-%L [font="Times]for(n=10; n>0; n--)
p?*Q- f [font="Times]System.out.println("tick " + n);
iIvc43YV% [font="Times]}
9%k2'iV7 [font="Times]}
zpzK>DH( 与上面那两个的区别,[font="Times]for循环执行的次数是可以在执行之前确定的。通俗一点说吧,看这个例子[font="Times] for(n=10; n>0; n--)就是在括号里的时候,就已经知道要循环[font="Times]10次了。
Cl5uS%g 还有啊,[font="Times]for循环的部分可以为空的
<->{ [font="Times]class ForVar {
o15-ZzE- [font="Times]public static void main(String args[]) {
"~#3&3HVS [font="Times]int i;
N,`$M.|? [font="Times]boolean done = false;
,KF'TsFf [font="Times]i = 0;
iNWw;_|1 [font="Times]for( ; !done; ) {
:WjpzgPuN [font="Times]System.out.println("i is " + i);
-c_74c50 [font="Times]if(i == 10) done = true;
viW!,QQ(S [font="Times]i++;
]}Mj)J" m [font="Times]}
US+Q~GTA [font="Times]}
.?D7dyU l1 [font="Times]}
循环语句的例子下载 `n.5f[wC [font="Times] 2.分支语句[font="Times]
^?-:'<4q$ [font="Times] if/else语句
Ye\rB\- [font="Times]class IfElse {
S{Kiy#ltWc [font="Times]public static void main(String args[]) {
61Bwb]\f/| [font="Times]int month = 4; // April
}d[ kxo [font="Times]String season;
bbtGXfI+SB [font="Times]if(month == 12 || month == 1 || month == 2)
dV*]f$wQ [font="Times]season = "Winter";
+dWDxguE{w [font="Times]else if(month == 3 || month == 4 || month == 5)
Y4OPEo 5o [font="Times]season = "Spring";
e{h<g>7 [font="Times]else if(month == 6 || month == 7 || month == 8)
rDD:7*z [font="Times]season = "Summer";
")_|69 VX [font="Times]else if(month == 9 || month == 10 || month == 11)
Hu^1[# [font="Times]season = "Autumn";
l\E%+?K+^ [font="Times]else
",p;Sd [font="Times]season = "Bogus Month";
$'0u |Xy` [font="Times]System.out.println("April is in the " + season + ".");
%r<rcY [font="Times]}
NC8t)
X7 [font="Times]}
0m7Y>0wC6T [font="Times]//这段程序输出[font="Times]:
4{}FL [font="Times]//April is in the Spring.
9?A)n4b; [font="Times]// 注意[font="Times] “[font="Times]||”是或运算
ko5 @qNq [font="Times] switch语句
)mI 05 [font="Times] class Switch {
45=bGf# [font="Times]public static void main(String args[]) {
dl.N.P7}4 [font="Times]int month = 4;
<vnHz?71c [font="Times]String season;
b1?#81 [font="Times]switch (month) {
teOe#* [font="Times]case 12:
s6ZuM/Q [font="Times]case 1:
QgrpBG [font="Times]case 2:
\n" {qfn`r [font="Times]season = "Winter";
j>*S5y.{ [font="Times]break;
3RiWZN [font="Times]case 3:
iMt:9|yF}8 [font="Times]case 4:
pe0F0Ruy [font="Times]case 5:
v&Ii^?CvO [font="Times]season = "Spring";
f&