我的if语句被忽略了。如何让程序识别它？

Question

我目前正在制作一个能够找到数字百分比的项目。但是，当我根据用户输入创建if语句来确定要执行的进程时，即使输入与if语句匹配，它也会跳到最后的else语句。这是我的代码。

public class Percentage {
public static void main (String[] args){
    Scanner input = new Scanner(System.in);
    System.out.println("Enter 'a' if you want to find a percentage of a given number.");
    System.out.println("Enter 'b' if you want to find how much percent of a given number is a certain number.");
    String choice = input.nextLine();


    if (choice == "a"){
        System.out.println("Enter the number.");
        float numA = input.nextFloat();
        System.out.println("Enter what percentage of the number you want to find.");
        float perA = input.nextFloat();
        float decA = perA * 0.01F;
        float outA = numA * decA;
        System.out.println(perA + "% of" + numA + "is: " + outA);
    } else if (choice == "b"){
        System.out.println("Enter the main number.");
        float mainB = input.nextFloat();
        System.out.println("Enter the number whose percentage of the main number you want to find.");
        float minB = input.nextFloat();
        float quoB = minB/mainB;
        float perB = quoB * 100;
        System.out.println(minB + "is" + perB + "% of " + mainB);
    } else {
        System.out.println("Invalid answer.");
    }

    input.close();
}

}

当我运行程序并输入a或b时，它直接转到else语句输出＆＃34;无效答案。＆＃34;我的代码有什么问题？