Java在同一行上打印字符串和int

Question

I was trying to print a string and int on a same line. But I get an error. I know my way around this error but why does the line System.out.println("This is a string: %i", c2.a); gives error whereas the line System.out.println("This is class method" + c2.a ); gives the correct output. Below is my code.

public class MyClass
{
  private int a;
  public double b;

  public MyClass(int first, double second)
  {
    this.a = first;
    this.b = second;
  }

  // new method
  public static void incrementBoth(MyClass c1) {
    c1.a = c1.a + 1;
    c1.b = c1.b + 1.0;
  }

  //pass by valuye therefore no change
  public static void incrementA(int a)
  {
    a = a+1;
  }

  public static void main(String[] args)
  {
    MyClass c1 = new MyClass(10, 20.5);
    MyClass c2 = new MyClass(10, 31.5);
    // different code below
    incrementBoth(c2);
    incrementA(c1.a);
    System.out.println("This is a object passing: %i",c2.a);
    System.out.println("This is object passing: " + c2.a );
    System.out.println("This is pass by value: %d",c1.a);
  }
}

My other question is does the line incrementBoth(c2) changes value of c2 because here whole object is passed to the method rather than passing by value in incrementA(c1.a)

Answer 1

You need to use the printf method and not println .

println is used to print primitive types, Strings and objects as they are. Also, println takes only one argument as input. That is the reason you are getting an error when you pass multiple arguments to it in your code.

printf on the other hand is used to format and then print the formatted string to the Standard output / error. This is what you should use in your code above for formatting the output.

Here's a reference to the tutorials .

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Hope this helps!