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HW0

约 269 个字 65 行代码 1 张图片 预计阅读时间 2 分钟

BJP5 Self-Check 1.26: Confusing

What is the output from the following Java program?

public class Confusing {
    public static void method1() {
        System.out.println("I am method 1.");
    }

    public static void method2() {
        method1();
        System.out.println("I am method 2.");
    }

    public static void method3() {
        method2();
        System.out.println("I am method 3.");
        method1();
    }

    public static void main(String[] args) {
        method1();
        method3();
        method2();
        method3();
    }
}

I am method 1.
I am method 1.
I am method 2.
I am method 3.
I am method 1.
I am method 1.
I am method 2.
I am method 1.
I am method 2.
I am method 3.
I am method 1.

BJP5 Exercise 2.5: starTriangle

Write for loops to produce the following output:

*
**
***
****
*****


for (int i=0;i<5;i++){
            for (int j=0;j<i;j++){
                System.out.print("*");
            }
            System.out.println('*');
        }

BJP5 Self-Check 2.25: numberTotal

alt text

  • total will be changing during the process. while the number is mounting / total is dropping -> as the number increases to 6, the sum will dropp to 4,which is smaller than the number

BJP5 Exercise 3.23: printIndexed

Write a method called printIndexed that accepts a String as its parameter and prints the String's characters in order followed by their indexes in reverse order. For example, the call of printIndexed("ZELDA"); should print Z4E3L2D1A0 to the console.
This is a method problem. Write a Java method as described. Do not write a complete program or class; just the method(s) above.

public static void printIndexed(String s){
    for (int i=0;i<s.length();i++){
        System.out.print(s.charAt(i)+String.valueOf(s.length()-i-1));
    }
}

**What I've learned? **
- a Method: public static void printIndexed(String s)
- s.charAt(i): same as s[i] in python
- String.valueOf() : same as str() in python
- remember: java is a language which is object-oriented. So we use s.length to mark the length of s

BJP5 Exercise 4.17: stutter

method problem√

Write a method called stutter that accepts a parameter and returns the String with its characters returns repeated twice. For example, stutter("Hello!") `returns` "HHeelllloo!!"

public static String stutter(String s){
    String str="";
    for (int i=0;i<s.length();i++){
        char c = s.charAt(i);
        String result = String.format("%c%c",c,c);
        str+=result;
    }
    return str;
}

what have learned?
- String result = String.format("%c%c",c,c); means double the string, using the format method

public static int quadrant(double x, double y){
    if (x==0.0 || y==0.0){
        return 0;
    }
    else if (x>0.0 && y>0.0){
        return 1;
    }
    else if (x<0.0 && y>0.0){
        return 2;
    }
    else if (x<0.0 && y<0.0){
        return 3;
    }
    else{
        return 4;
    }
}

Note:

  • else if instead of elif in python
  • or → ||
  • 0.0 is actually double

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