局部变量、实例字段、输入参数和类字段有什么区别? [英] What is the difference between a local variable, an instance field, an input parameter, and a class field?

问题描述

对于一个简单的 Java 程序来说，局部变量、实例字段、输入参数和类字段有什么区别?

What is the difference between a local variable, an instance field, an input parameter, and a class field with respect to a simple Java program?

推荐答案

局部变量是在块的范围内定义的.它不能在该块之外使用.

A local variable is defined within the scope of a block. It cannot be used outside of that block.

示例:

if(x > 10) {
    String local = "Local value";
}

我不能在 if 块之外使用 local.

I cannot use local outside of that if block.

实例字段，或字段，是绑定到对象本身的变量.我可以在对象中使用它而不需要使用访问器，并且对象中包含的任何方法都可以使用它.

An instance field, or field, is a variable that's bound to the object itself. I can use it in the object without the need to use accessors, and any method contained within the object may use it.

如果我想在对象的外部使用它，并且它不是public，我将不得不使用 getter 和/或 setter.

If I wanted to use it outside of the object, and it was not public, I would have to use getters and/or setters.

示例:

public class Point {
    private int xValue; // xValue is a field

    public void showX() {
        System.out.println("X is: " + xValue);
    }
}

输入参数，或参数，甚至参数，是我们传递给方法或构造函数的东西.它具有与我们传递给它的方法或构造函数相关的范围.

An input parameter, or parameter or even argument, is something that we pass into a method or constructor. It has scope with respect to the method or constructor that we pass it into.

示例:

public class Point {
    private int xValue;
    public Point(int x) {
        xValue = x;
   }

    public void setX(int x) {
        xValue = x;
    }
}

两个 x 参数绑定到不同的作用域.

Both x parameters are bound to different scopes.

一个类字段，或静态字段，类似于一个字段，但不同的是你不需要有包含对象的实例来使用

A class field, or static field, is similar to a field, but the difference is that you do not need to have an instance of the containing object to use it.

示例:

System.out.println(Integer.MAX_VALUE);

我不需要 Integer 的实例来检索所有整数的全局已知最大值.

I don't need an instance of Integer to retrieve the globally known maximum value of all ints.

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