我还是有点新，所以我将包括我所有的java代码，然后解释我在寻找什么
import java.util.Scanner;
public class Part_I{
public static Scanner input = new Scanner(System.in);
public static String strInfo;
public static int number;
public static void main(String[] args){
String presidents[][] = {
{"1 ","George"," ","Washington"," (1789-1797) ","John Adams"},
{"2 ","John"," ","Adams"," (1797-1801) ","Thomas Jefferson"},
{"3 ","Thomas"," ","Jefferson"," (1801-1809) ","Aaron Burr"},
{"4 ","James"," ","Madison"," (1809-1817) ","George Clinton"},
{"5 ","James"," ","Monroe"," (1817-1825) ","Daniel D. Tompkins"},
{"6 ","John"," Quincy ","Adams"," (1825-1829) ","John C. Calhoun"},
{"7 ","Andrew"," ","Jackson"," (1829-1837) ","John C. Calhoun"},
{"8 ","Martin"," Van ","Buren"," (1837-1841) ","Richard M. Johnson"},
{"9 ","William"," Henry ","Harrison"," (1841) ","John Tyler"},
{"10 ","John"," ","Tyler"," (1841-1845) ","None"},
{"11 ","James"," K. ","Polk"," (1845-1849) ","George M. Dallas"},
{"12 ","Zachary"," ","Taylor"," (1849-1850) ","Millard Fillmore"},
{"13 ","Millard"," ","Fillmore"," (1850-1853) ","None"},
{"14 ","Franklin"," ","Pierce"," (1853-1857) ","William King"},
{"15 ","James"," ","Buchanan"," (1857-1861) ","John C. Breckinridge"},
{"16 ","Abraham"," ","Lincoln"," (1861-1865) ","Hannibal Hamlin"},
{"17 ","Andrew"," ","Johnson"," (1865-1869) ","None"},
{"18 ","Ulysses"," S. ","Grant"," (1869-1877) ","Schuyler Colfax"},
{"19 ","Rutherford"," B. ","Hayes"," (1877-1881) ","William Wheeler"},
{"20 ","James"," A. ","Garfield"," (1881) ","Chester Arthur"},
{"21 ","Chester"," ","Arthur"," (1881-1885) ","None"},
{"22 ","Grover"," ","Cleveland"," (1885-1889) ","Thomas Hendricks"},
{"23 ","Benjamin"," ","Harrison"," (1889-1893) ","Levi P. Morton"},
{"24 ","Grover"," ","Cleveland"," (1893-1897) ","Adlai E. Stevenson"},
{"25 ","William"," ","McKinley"," (1897-1901) ","Garret Hobart"},
{"26 ","Theodore"," ","Roosevelt"," (1901-1909) ","None"},
{"27 ","William"," Howard ","Taft"," (1909-1913) ","James S. Sherman"},
{"28 ","Woodrow"," ","Wilson"," (1913-1921) ","Thomas R. Marshall"},
{"29 ","Warren"," G. ","Harding"," (1921-1923) ","Calvin Coolidge"},
{"30 ","Calvin"," ","Coolidge"," (1923-1929) ","None"},
{"31 ","Herbert"," ","Hoover"," (1929-1933) ","Charles Curtis"},
{"32 ","Franklin"," D. ","Roosevelt"," (1933-1945) ","John Nance Garner"},
{"33 ","Harry"," S. ","Truman"," (1945-1953) ","None"},
{"34 ","Dwight"," D. ","Eisenhower"," (1953-1961) ","Richard Nixon"},
{"35 ","John"," F. ","Kennedy"," (1961-1963) ","Lyndon B. Johnson"},
{"36 ","Lyndon"," B. ","Johnson"," (1963-1969) ","None"},
{"37 ","Richard"," ","Nixon"," (1969-1974) ","Spiro Agnew"},
{"38 ","Gerald"," ","Ford"," (1974-1977) ","Nelson Rockefeller"},
{"39 ","Jimmy"," ","Carter"," (1977-1981) ","Walter Mondale"},
{"40 ","Ronald"," ","Reagan"," (1981-1989) ","George Bush"},
{"41 ","George"," ","Bush"," (1989-1993) ","Dan Quayle"},
{"42 ","Bill"," ","Clinton"," (1993-2001) ","Al Gore"},
{"43 ","George"," W. ","Bush"," (2001-2009) ","Dick Cheney"},
{"44 ","Barack"," ","Obama"," (2009-2017) ","Joe Biden"},
};
System.out.println("This will display the President and VP of the United States based on the number you provide.");
System.out.println("Please enter a number between 1 and 44 to see information or q to quit: ");
strInfo = input.nextLine();
while(strInfo != "q"){
if(isInteger(strInfo)){
number = Integer.parseInt(strInfo);
if (number >= 1 && number <=44){
System.out.println();
System.out.println(presidents[number-1][0] + "President " + presidents[number-1][1] + presidents[number-1][2] + presidents[number-1][3] + presidents[number-1][4] + "Vice President " + presidents[number-1][5]);
System.out.println();
System.out.println("Please enter a number between 1 and 44 to see information or q to quit: ");
strInfo = input.nextLine();
}else{
System.out.println();
System.out.println("Wrong Input! Please enter number 1-44 or q to quit.");
strInfo = input.nextLine();
}
}else{
System.out.println();
System.out.println("This program has been terminated. Good Bye!");
System.exit(0);
}
}
}
public static boolean isInteger(String strInfo){
if (strInfo == null) {
return false;
}
int length = strInfo.length();
if (length == 0) {
return false;
}
int i = 0;
if (strInfo.charAt(0) == '-') {
if (length == 1) {
return false;
}
i = 1;
}
for (; i < length; i++) {
char c = strInfo.charAt(i);
if (c < '0' || c > '9') {
return false;
}
}
return true;
}
}
我主要关心的是while循环。
while(strInfo != "q"){
if(isInteger(strInfo)){
number = Integer.parseInt(strInfo);
if (number >= 1 && number <=44){
System.out.println();
System.out.println(presidents[number-1][0] + "President " + presidents[number-1][1] + presidents[number-1][2] + presidents[number-1][3] + presidents[number-1][4] + "Vice President " + presidents[number-1][5]);
System.out.println();
System.out.println("Please enter a number between 1 and 44 to see information or q to quit: ");
strInfo = input.nextLine();
}else{
System.out.println();
System.out.println("Wrong Input! Please enter number 1-44 or q to quit.");
strInfo = input.nextLine();
}
}else{
System.out.println();
System.out.println("This program has been terminated. Good Bye!");
System.exit(0);
}
}
}
我想让它，所以它的任何字符串，除了什么能够被转换为int或"q"会说错误的输入，让你输入另一个字符串值。现在，任何字符串都会使程序终止。我应该在while循环中改变什么我应该如何改变它或者它应该是什么样子的这样如果字符串输入不是q或者可转换为int会显示错误的输入并再次要求输入?
这将帮助你实现你想要做的事情
while (!strInfo.equals("q")) {
if (isInteger(strInfo)) {
number = Integer.parseInt(strInfo);
if (number >= 1 && number <= 44) {
System.out.println();
System.out.println(presidents[number - 1][0] + "President " + presidents[number - 1][1] + presidents[number - 1][2] + presidents[number - 1][3] + presidents[number - 1][4] + "Vice President " + presidents[number - 1][5]);
System.out.println();
System.out.println("Please enter a number between 1 and 44 to see information or q to quit: ");
strInfo = input.nextLine();
} else {
System.out.println();
System.out.println("Wrong Input! Please enter number 1-44 or q to quit.");
strInfo = input.nextLine();
}
} else {
System.out.println();
System.out.println("Wrong Input! Please enter number 1-44 or q to quit.");
strInfo = input.nextLine();
}
}
System.out.println();
System.out.println("This program has been terminated. Good Bye!");
System.exit(0);
您不应该使用"="one_answers"!="等普通操作符检查字符串是否相等。使用String .equals()方法。
第一行应该是
while(!strInfo.equals("q"))
更多信息:
http://www.leepoint.net/data/expressions/22compareobjects.html你的代码不工作的原因是因为你试图比较两个字符串的内容是否相等使用==操作符(这只比较如果两个引用指向相同的对象)。==操作符不会比较两个字符串的内容。
为了使您的代码工作，您需要使用 = 来比较两个字符串的内容，如下所示:
while(!strInfo.equals("q"))
现在让我们试着深入研究为什么你的代码不能工作。为此，我们需要理解== &=
==操作符用于比较其两侧的两个引用是否都指向同一对象(基本上可以说它类似于比较引用所指向对象的地址)。
而对于String， = 比较两个String的内容。类的创建者有责任重写默认的equals方法，以便根据对象的意义来比较该类的对象。例如，在String类的情况下，类的创建者已经重写了equals方法来比较字符串的内容。
String a = "test"; // lets say the object guy has address : 24
String b = a; // now b points to the same object that is being referenced by a
System.out.println(a == b); // this will be true as both point to the same reference
System.out.println(a.equals(b)); // this will be true as the contents of both these strings is the same.
// Now lets consider a new strings having same content "test"
String c = "test";
System.out.println(a == c); // this will be false as both point to the different references or memory location
System.out.println(a.equals(c)); // this will be true as the contents of both these strings is the same.