Java练习一
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互联网集市收集整理的这篇技术教程文章主要介绍了Java练习一，小编现在分享给大家，供广大互联网技能从业者学习和参考。文章包含5400字，纯文字阅读大概需要8分钟。
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Java编码示例
各种java程序来说明多种概念。
- 输出hello world
/Hello,world
/
public class HelloWorld{
public static void main(String[] args){
System.out.println("Hello,world");
}
} -
如何在同一个类中调用方法的示例
/CallingMethodsInSameClass.java
说明如何在同一个类中调用静态方法
*/
public class CallingMethodsInSampleClass{
public static void main(String[] args){
printOne();
printOne();
printTwo();
}public static void printOne(){ System.out.println("Hello world"); } public static void printTwo(){ printOne(); }}
-
使用for循环计算阶乘的简单示例。使用内置的int数据类型只有显示13！
public class Factorial{
public static void main(String[] args){
final int NUM_FACTORS = 100;
for(int i < 0; i < NUM_FACTORS; i ++)
{
System.out.println(i + "! is" + factorial(i));
}
}public static int factorial(int n){ int result = 1; for(int i = 2;i < =n ;i++){ result *= i; } return result; } } -
增强的循环
public class EnhancedFor{
public static void main(String[] args){
int[] list = {1,2,3,4,5,6,7,8,9};
int sum = sumListEnhanced(list);
System.out.println("Sum of elements in list: " + sum);System.out.println("Original List"); printList(list); System.out.println("Calling addOne"); addOne(list); System.out.println("List after call to addOne"); printList(list); System.out.println("Calling addOneError"); addOneError(list); System.out.println("List after call to addOneErrro.Noete elements of list did not change"); printList(list); } //使用加强的循环语句,进行求和 public static int sumListEnhanced(int[] list){ int total = 0; for(int var:list){ total += var; } return total; } //使用传统的循环,进行求和 public static int sumListold(int[] list){ int total = 0; for(int i = 0; i < list.length; i++){ total += list[i]; System.out.println(list[i]); } return total; } //下面的代码好像是给每个元素加1,实际上并没有 public static void addOneError(int[] list){ for(int val:list){ val += 1; } } //给每个元素加1 public static void addOne(int[] list){ for(int i = 0; i < list.length; i++){ list[i] += 1; } } //打印每个数组 public static void printList(int[] list){ System.out.println("index, value"); for(int i = 0; i<list.length;i++){ System.out.println(i + ", "+ list[i]); } } } -
显示值参数行为的例子。在Java中，所有参数都是按照值进行传递
public class PrimitiveParameters{
public static void main(String[] args){
go();
}public static void go(){ int x = 3; int y = 2; System.out.println("In method go. x:" + x +" y: "+y); falseSwap(x,y); System.out.println("In method go. x:" + x +" y: "+y); moreParameters(x,y); System.out.println("In method go. x:" + x+ " y: "+y); } public static void falseSwap(int x,int y){ System.out.println("In method go. x:" + x +" y: "+y); int temp = x; x = y; y = temp; System.out.println("in method falseSwap. x:"+x + "y:"+y); } public static void moreParameters(int a, int b){ System.out.println("in method falseSwap. a:"+a + " b:"+b); a = a*b; b = 12; System.out.println("in method falseSwap. a:"+a + " b:"+b); falseSwap(b,a); System.out.println("in method falseSwap. a:"+a + " b:"+b); } } //下面是执行结果 In method go. x:3 y: 2 //初始化x=3,y=2 In method go. x:3 y: 2 //执行falseSwap函数，以在函数内成功调整两数值 in method falseSwap. x:2y:3 In method go. x:3 y: 2 //执行完falseSwap函数并没有交换两值 in method falseSwap. a:3 b:2 //执行moreParameters in method falseSwap. a:6 b:12 In method go. x:12 y: 6 in method falseSwap. x:6y:12 in method falseSwap. a:6 b:12 In method go. x:3 y: 2 //对两个实际值并没有改变 -
一些String操作的简短例子
public class StringExample{
public static void main(String[] args){
String s1 = "Computer Science";
int x = 307;
String s2 = s1 + " " +x;
String s3 = s2.substring(10,17);
String s4 = "is fun";
String s5 =s2 + s4;System.out.println("s1: "+s1); System.out.println("s2: "+s2); System.out.println("s3: "+s3); System.out.println("s4: "+s4); System.out.println("s5: "+s5); x = 3; int y = 5; String s6 = x + y + "total"; String s7 = "total" + x + y; String s8 = ""+x+y + "total"; System.out.println("s6: "+s6); System.out.println("s7: "+s7); System.out.println("s8: "+s8); } } //执行结果 //Java编译器是从左到右处理表达式的，s6第一个表达式x+y的话就是Java编译器理解为运算符，而第二和第三则理解为连接符 s1: Computer Science s2: Computer Science 307 s3: cience s4: is fun s5: Computer Science 307is fun s6: 8total s7: total 35 s8: 35 total -
一个程序，包含各种Java语法的示例，它将10进制转化2进制
public class BinaryConverter{
public static void main(String[] args){
for(int i = -5;i<32;i++){
System.out.println(i+": "+ toBinary(i));
System.out.println(i);
System.out.println(i+": "+Integer.toBinaryString(i));
}
}//在base2中返回一个base10 num的字符串 public static String toBinary(int base10Num){ boolean isNeg = base10Num < 0; // 优先级，先计算<，base10Num小于0为真 base10Num = Math.abs(base10Num); //返回绝对值Math.abs() String result = ""; while(base10Num > 1){ //以base10Num等于11为例子，result = 11%2+ ' ' = '1' //base10Num/2 = 5 //result = 5%2 + '1'='11' //base10Num/2=1 //result = 1%2 +'11'='011' //base10Num = 1 result = (base10Num %2) + result; base10Num /= 2; } //断言 asser condition:expr;检查值是否等于0或1 assert base10Num == 0 || base10Num == 1:"value is not <= 1: "+base10Num; //还是以11为例，经过上面的循环,result='011'，base10Num=1 //最终result=1011 result = base10Num + result; //断言 assert all0sAndls(result); //如果是false，不执行。正数不执行，负数执行 if( isNeg ) result = "-" + result; return result; } public static boolean all0sAndls(String val){ //判断result是否有结果 assert val != null: "Failed precondition all0sAndls.parameter cannot be null"; boolean all = true; int i = 0; char c; //判断每个位置是否是0或1 while(all && i < val.length()){ //charAt() 方法用于返回指定索引处的字符。 c = val.charAt(i); all = c == '0' || c == '1'; i++; } return all; } }
原文：https://www.cnblogs.com/yihang996/p/11489641.html
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