请问ArkTS中this使用场景是什么？

class A { 
  count: string = 'a'; 
  m(i: string): void { 
    this.count = i; 
  } 
} 
 
function main(): void { 
  let a = new A(); 
  console.log(a.count);  // 打印a 
  a.m('b'); 
  console.log(a.count);  // 打印b 
}

class Test1 { 
  value: string = ''; 
  constructor (value: string) { 
    this.value = value; 
  } 
  foo() { 
    console.log(this.value); 
  } 
} 
 
let obj: Test1 = new Test1('abc'); 
obj.foo();